You seem to be doing the right thing.
I won't claim this is true everywhere, but most Universities have procedures to revise an error in grades including after the course is over, if indeed an error was made. So don't add to your stress by feeling all is lost if you can't sort it out right now; though of course it of course there is additional stress from uncertainty and feeling under the gun.
Based on what you say, it is bad form for your professor to not reply and not show up. What are other vehicles to "get help" in the course prior to the exam? TAs? Review sessions? If there are none and the prof is nonresponsive, that in my mind is actually a bigger issue than a single grade.
Practically, two suggestions:
Have you adequately (but briefly) described what is the issue -- and the urgency -- in your email? An email of "Dear Prof X. Will you be at office hours next ...., I have a question?" may well be ignored as "don't ask silly questions" (and when they unexpectedly can't make that office hour there being no recollection of it to follow up with you). A more effective email would be "Dear Prof X. I came to your office hours on ... but you seems you weren't able to make it. I've discovered a rather serious grading discrepancy that it would be very helpful to sort out before the exam and end of course. When could I come see you?" It's more difficult to ignore -- and also lays a more compelling paper trail if you do need to appeal your grade after the course.
Have you tried other communication channels? Again, the prof should be responsive. But too often we double down on what should work but doesn't. Try phoning and leaving a voicemail. Leave a paper note under their door AND at their department office reception. Talk to the TA, if any.
Finally, as a former lecturer, it's worth noting: it's crazy how many students want last minute help, often are confrontational due to their own stress, and can't formulate a reasonable question without it being clear they were paying no attention during the course until the last minute. I see no reason to assume you're part of this crowd, but think through your communications how to ensure you're not coming across that way. You have an important, concrete issue to discuss. Make sure you communicate that even if your email arrives sandwiched between 3 other student emails saying "can I ask you some questions, not sure what yet, during office hour?", "can you tell us more what's on the final exam", and "can I hand in my assignment 2 months late?". Good luck!