if cannot masterbate how will cope having sex?

Okay . . . quite embarassed at saying all this but here goes. I am a fifteen yr old girl and i started masterbating a while back but i don't do it very often. I do find pleasure from rubbing my clit but whenever i have tried to . .. ahem . . .finger myself i can't physically get even one finger in more than one inch. Ive also had problems with getting tampons in and don't use them. I am a virgin and haven't got far with a guy before, is that the only reason? If so what if they can't um 'get in' either? I've tried relaxing and pleasuring myself so that i am wet first but it doesn't happen. Thing is what happens when i first have sex . . ii mean a penis is somewhat larger than one inch of finger . . .. please can someone reassure me that i am not abnormal or if i am what to do about it.