This is what I understand. There is a girl who you like but you are wondering whether you should take a chance with the relationship that she thinks has good potential. But the problem is is that you are wondering whether or not you should go for it. What I'm not really understanding is: "I'm also sick of making exceptions." This part is the vague part. What kind of exceptions?
With the information you are giving me, this is what I think. I think one should always try things. Better regret it later than to have never tried at all. I mean, what if your relationship with her ends up being one of the best things that has ever happened to you? It would be a shame to miss out on what would be magical just because of uncertainty.
But, if you find yourself unhappy with the relationship, and with her, please pull out of the relationship. It is not good for you and neither for her. People who endure the suffering just because they are scared to stop the relationship are miserable people in the end. It's ok to move on. If you don't, you are only hurting her more.
Especially if it is early in the relationship, f you are not feeling it, and she maybe is, you are leading her on. She will fall hard and by the time you act on your feelings you will hurt her more than you would have if you had just broken it off to begin with.
Just be frank with her. Try out the relationship with her. Take the risk. But see how you feel at first, test the waters. That will determine the future you two will have. If you like it then that's good, if you don't, there are plenty more fish in the sea. But don't risk letting the best fish go because you are afraid to fish to begin with :D