No-one is perfect and, during the teens, emotions can get out of control.
You did something that you feel you shouldn't have and now you feel guilty.
You are still blaming yourself and you think that your friends are still blaming you, too ~ even though they assure you that they aren't.
Going over it with them 100 times, by text, probably won't help ~ it may just irritate them.
All you can do is apologise, just once, but properly ~ say how guilty and sad that you feel ~ whether or not they still blame you ~ and say that you wish that there was something that you could do to change things, but you can't and you just hope that they will forgive and forget, and that you can still be good friends.
Maybe they truly have got over it, but, if not, a quiet serious face-to-face discussion, next time you meet up, rather than texting, could be the answer.
As you say, what's done is done ~ you have tried to be friendly and there is not much more that you can do.
I'm sure that they will come around eventually ~ you seem like a lovely friendly girl
Good luck, try not to worry about it and keep smiling
PS. If this is making you feel really down, then perhaps you should talk to your parents about it, and tell them just how much it is worrying and upsetting you