How do I fix this (Her parents)?

Well... I say you go to her house one day and before you say hi or say anything just say "can we just try to reason with this? i love your daughter and so do you, so we both have something to fight for" and explain to them that you love her, and you both felt it was time to show this love to each other by *making love* don't say by having .. and just basically tell them that you're not the guy they think you are and to give you a chance, it's been 3 weeks so they've cooled down. I had a very similar situation and my parents accepted the guy back.. if they really love they're daughter they'll take you into they're house.. good luck!