This sounds like it's a cell formatting issue. Make sure your Room Number
column is formatted as Text and not General or Number.
This is from LibreOffice, but the behaviour is the same for Excel as long as the cell is formatted as Text.
Based on your comment that you simply custom formatted the value to show a leading 0, you can use this formula to check if there is a leading 0 on a room name and then add one if there isn't:
=IF(LEFT(A1,1)=0,LEFT(A1,2),CONCAT("0",LEFT(A1,1)))