Wel I'm just as bad so not much advice but you did mention that she says her past bf's wer meaningless and that would make me worse because I know thats not possible, you have to have some feelings about past relationships, you may have loved them or hated them but you have to feel something, and the fact that she says it means nothing shows she will lie to make you happy and that she doesn't really get you, honesty may hurt but is easier to get over, because you know you can fully trust her.
The penis size thing:
Well thats new for men isn't it, basically its the same as women and their entire bodies, she should relate, I mean women get evrythin compared to evry woman on the tv or street, not just their vaginas. She is probably way more insecure about her body than you are.