Do not marry. If you were more experienced, you would've left her already, because you two obviously are not a good fit. But breaking up is very hard- it almost seems unimaginable the first time... But you will appreciate it afterwards. If you stay with her, that uncomfortable and unhappy feeling that never quite leaves you will only get stronger, until the relationship finally does end, only now you've wasted another five years (or whatever) of your life.
Get out. Now. You have a lot of growing up to do, and once you begin you'll think you were insane for ever putting up with this woman.