Is there somthing wrong with my girlfriends vagina?

She and I have been dating for over a year and over the past week we have tried to have sex twice.(both of us for the first time).We make out for like 2 hours and fool around and oral and what not,so by the time were ready to have sex she is plenty moist.The only problem is i cant seem to get it in more then like an inch.I dont have a big penis 7 inches fully erect,and its not really that wide so it cant be me.Does having more sex fix this problem or does she just have a small vagina?