Whenever I struggle with a tosafos I take a look on the daf yomi website here
It writes about the said tosafos as follows:
TOSFOS DH TAFAF GINA'OS
תוספות ד"ה טפף גינאות
(SUMMARY: Tosfos explains that these are level gardens.)
פי' גינות שוות שבנויות בנין שוה שאין תוספת ומגרעת בזה ובזה כמו הלוך וטפוף תלכנה (ישעיה ג) וכמו (יומא דף מח.) מדה לא מחוקה ולא גדושה שנקראת טפופה.
(a)
Explanation: These are level gardens. They are built evenly, without protrusion or indentation deficiency in this (direction) or in this, like "Haloch v'Tafof Telachnah", and a measure that is not leveled off or heaping, which is called Tefufah.
- Note: This is from the Aruch, who explains that the measure is exactly even. "Lo Mechukah" means that one did not level it off with a bar that sags in the middle and descends into the measure and removes some contents below the walls, which causes that the measure is deficient.
This is how it links in with the earlier point that when moshiach come these gardens will likewise be balanced and of equal measures.
EDIT
It is worth noting the Parshas Derachim 7:13 which comprehensively sheds more light on the Gemara in Bava Basra and its relation to Moshiach. It seems to be saying that when Moshiach comes Yerushalayim will expand beyond measure:
My translation:
And it is well known that this psalm was spoken by Dovid concerning the building of the third house (i.e. the Thrid Beis Hamikdash), like it is brought in the Midrash and like the commentaries similarly write. And it says in Perek HaSfina (Bava Basra 75b); "Reish Lakish says: In the future, the Holy One, Blessed be He, will add to Jerusalem one thousand times the numerical value of tefaf of gardens; one thousand times the numerical value of kefel of towers...And each and every one of these additions will be like the great city of Tzippori in its prosperity." And Rabbi Yosi says; "I saw Tzippori in its prosperity, and there were one hundred and eighty thousand markets of sellers of meat sauces in it. (On this basis, one can estimate the future size of Jerusalem.)"
And it says in the Midrash that which it writes in Shir HaShirim 7:5 - "Your nose is like the Lebanon tower that faces toward Damascus." which teaches that in the future the gates of Yerushalayim will reach as far as Damasacus. And it says in the Midrash (Sifrei, Devarim 1) "A pronouncement: The word of the LORD. He will reside in the land of Hadrach and Damascus" (Zecharia 9:1) - Rabbi Yehuda expounded: This ("chadrach") refers to the Messiah who will be "chad" ("sharp") to the Canaanites, and "rach" ("soft") to Israel" — whereupon R. Yossi b. Dormaskith said to him: Yehudah, why do you distort the verses for us? I testify by heaven and earth that I am from Damascus and there is a place called Chadrach there. And how do I understand "and Damascus is (its) resting place"? (As meaning) that Yerushalayim is destined to extend until Damascus; "(its) resting place" is Jerusalem, as it is written (Psalms 132:19) "This (Jerusalem) is My resting place forever." And similarly it says: "Your nose is like the Lebanon tower that faces toward Damascus".
Furthermore it is brought in the Midrash that in the future Jerusalem will reach to the ocean. And the Abarbanel already brings this in his explanation on Yeshaya (siman 49). And it is related in Perek HaSfina (Bava Basra 75b) "Rabbi Ḥanina bar Pappa says: The Holy One, Blessed be He, wished to give a set measure for Jerusalem, as it is stated (Zechariah 2:6): “(And I lifted up my eyes and saw, and behold a man with a measuring line in his hand.) Then I said: Where are you going? And he said to me: To measure Jerusalem, to see what is its breadth, and what is its length. The ministering angels said before the Holy One, Blessed be He: Master of the Universe, You have created many cities in Your world for the nations of the world, and You did not give the measure of their length or the measure of their width, (i.e., they are not limited by any set measure, but expand as they develop). With regard to Jerusalem, which has Your name in it, and Your Temple in it, and righteous people in it, will You give it a measure? Immediately: (“And, behold, the angel that spoke with me went forth, and another angel went out to meet him,) and said to him: Run, speak to this young man, saying: Jerusalem shall be inhabited without walls for the multitude of men and cattle".
And Rashi explains on the words "Jerusalem shall be "פְּרָזוֹת" - inhabited without walls" - Just as these "פְּרָזוֹת - prazos" that don't have any measure in the building but are like the ones who want to build - so too the same is for Yerushalayim. Thus the matter is known that these "פְּרָזוֹת" are cities without walls and Hashem promises us that Jerusalem in the future will be like these פְּרָזוֹת that don't have any measurements and it is in the greatness of its vast expanse.
