Small things aren’t small

I feel bad over small things in life. Normal things for a lot of people I would say. Most of it comes from little mistakes, like I don’t accept em. I think a lot before doing anything especially abt money so if I make a mistake I feel terribly sorry and angry and sad. For example last week I bought a pair of running shoes, I liked em and they were expensive. The guy at the store told me I could use em and if they weren’t right for me I could take em back. I used em for 2 walks and my right foot was really hurting, only using these shoes. So today I took em back to the store but the guy wasn’t there and the manager told me I can’t give them back if I used em. I feel like a total idiot and I just lost 230$ on some bs I can’t even use. I should have known better. This happens for a lot of things like if I don’t invest my money in the best way I start hating on the bank guy who manages my money and I feel stupid for trusting him. These things makes me feel so bad I’d stop doing everything just not to make mistakes