You are doing an amazing thing! Even if you go through the evaluation & decide it's not something you can do, you have that much more info to give someone else that considers living donation.
Every medical person you see from now through surgery is on your team. They want to make sure YOU can safely donate and live a long healthy life afterwards. They will test more things than you knew were possible to test, both physical & mental. I still think the evaluation process was harder than the actual donation!
You can decide at any time not to follow through with donation.
If at some point down the road, you need a kidney, you will go to the top of the list for recipients.