Made a mistake at work

I am the type of person where mistakes haunt me lol.

I am about 5 months into a job and I work as an academic advisor but really it is a call center but whatever. Anyway I had someone call and from there account it looked like I had to charge them 250 for a new course but then our finance team looked into it and I really have to charge them 745 since they didn’t pay for half of the course. I asked yesterday if they paid and they said yes and I wasn’t sure from their account.

I guess I know now. I told my boss I wrote that down for the future. I don’t think it’s something I’ll get fired for and I work really hard and diligently at my job it’s just I missed this one thing. It’s not a huge deal because he wasn’t charged just yet. So I just have to call the customer back and get the correct amount.

Idk I’m still learning new things everyday at this job