How do i explain this?

me and my girlfriend are both 15 and we were texting dirty when her mom apparently walked in, took her phone and read the messages (it wasn't as bad as it could have been) and called me saying we aren't ever allowed to date again unless i come to her house and explain why i said some things. what should i say? i was being a stupid hormonal 15 year old boy? (she would just call it an excuse) help?