Not a TIFU.

You did the best you could in the circumstances you were in with the knowledge you had. You can't be faulted for that.

It's possible.

Still, Its a serious thing and banks don't like people committing fraud, even if it's on accident or unintentional or whatever.

You didn't defraud yourself. You had 80 bucks and you still do. Instead, you have 80 worth of stuff and the bank has 80 bucks less.

What exactly do you think fraud is if you don't think it has to do with lying to banks to gain money?

Unfortunately, there is no easy out here, because fraud is a serious crime and being stupid or having a bad memory aren't solid defenses to it. You don't get to say you spent all this money but you forgot you did it so you should get all the money back and still keep the stuff.

How would the world function if that was OK?

You can take no action and hope they don't find out what happened. That could work out poorly if they can prove you got the stuff you spent the 80 on.

You could tell them to take their 80 back and hope you don't get entered into systems as a know fraud person.

Best case banks will think you are a bad risk, because you totally are.

Banks can get you for fraud now.