She thinks I'm rejecting her

Honestly, find a different girl. If she can't respect your time and gets upset because you have other plans that you prioritize she'll be that way forever. You'll have to cave on anything you found important without her and lose who you are now, you know the guy BEFORE she was even an issue.

Be firm, don't waiver and go about your usual plans. If she leaves, good riddance...

 

I know one thing I will not compromise when I do get in a relationship and that's my gym time but then again I would want to find someone who will go with me lol

 

WOW she's mad because you have a life and cannot be at her beck and call WOW . I have seen this before many times it never gets better ditch this one if there getting mad at this point IT GETS WORSE, You want someone that is flexible and kind not mean this is big red flag saying RUN.
FIND SOMEONE WHO LIKES YOU AS YOU ARE its good that you valued your time ,your on the right path get rid of this one

 

Apologise and find a time that works.

 

Did you tell her that you thought the timing was a bit of a squeeze? Did you offer a different day to reschedule? Did you tell her that you want to make this work?

This just seems like a miscommunication problem.