Saying sorry is so very hard ... I think it would be easier to buy her a pony !!! Saying sorry is really brave and you should do that then .... It's a stupid hard thing to say though. I should be saying sorry to someone right now and I don't wanna... I'm just gonna avoid life for a while then :)
First off, apologize sincerely. Give her a hug and tell her you love her.
As it has already been said you apologize. And you learn your lesson. Whatever you said or did had consequences that not only affected you but someone you love. Be more mindful of that next time.