Why Is My girlfriend acting like this?

So last night I was online talking to my girlfriend of nearly 2 years and everything was going great. Then she see’s a survey I did on my myspace that asked the question “Have You Ever Made Out On Your Tailgate”…well I had answered “Wouldn’t exactly say made out”…so like I said we where talking and happy then all of a sudden she puts that question up and accuses me of something. I told her I meant that I had kissed a girl on my tailgate once when I was 15 years old. It kinda upset me pretty bad that she’d think any thing else because she knew that I was never in a serious relationship before her and up until her I was actually a virgin. So her thinking I went further than a kiss hurt pretty bad. Well we’ve been fighting before this and she had told me last night that she was ok she had been thinking and everything was fine now. Well I kinda got mad and said it was kinda two faced of her to act like everything was ok when clearly it wasn’t. So she left without saying anything. Did I do anything wrong? I’ve sent her 10 appologies today and still haven’t got nothing.