I have severe social anxiety to the point I was essentially forced to drop out of college.

There's this small comic store where I live ran by a few friends. It was one of my favourite stores when I was a cringy 13 year old weeb. The store is still fantastic and I would like to visit sometimes, but I keep getting an overwhelming sense of guilt everytime I think about it.

2016ish I was hyperfixating on the manga Tokyo Ghoul, and this store was the only place I could buy the manga at a reasonable price without having to spend a ton on shipping. Every week they'd have the new volume. Because of storeage stuff, it was moved to every two weeks.

I was with my friends at the time, and upon seeing they didn't have the new volume, I started yelling. Not at anyone, just very loudly complaining about "how I was looking forward to this" and "I've had such a rough week at school", selfish kid stuff like that. I had anxiety back then, too, but I was so angry and caught in the moment.

When I went back downstairs, the clerk very calmly informed me that thayve changed it to every two weeks, that they're sorry. To which I nodded and said sorry for yelling. 

This was six years ago and the guilt still eats me alive. I feel so ashamed for how I acted, and I want to properly apologise for my behaviour, but I really don't know how to approach it. I know logically I could just go in with a simple "Sorry", but that doesn't feel sincere? I was considering buying an apology gift and writing a small letter saying how sorry I am, but I really don't know.

Talking to cashiers is one of my biggest struggles with anxiety, which is what's making this so much harder I think.