HELP! I made a BIG mistake during an interview!

Hello everyone. I had an interview with a job today. They asked what my GPA in undergrad and grad was. Unfortunately, I did not prepare myself for this question and did not know. Because of this, I irresponsibly gave an estimate of what i believed it was. I got in my car and immediately checked my transcripts. My undergrad GPA is 3.06, but i told them 3.1. My graduate GPA is 3.1 but I thought them 3.4 (it was actually 3.6 but I forgot about this one class that whooped my entire ass and made my GPA plummet) 3.0 to 3.1 isn’t horrible but 3.1 to 3.4 is a huge gap which makes me damn near want to pass out lol.

I’m going to send them an email with the correct GPA as well as attach a copy of my transcripts, but i wanted to know how I should word it? I don’t want them to think I am a liar. It was an honest mistake based on my lack of preparation.