"I often get 'stuck' going over everything I should have done differently/better/faster/whatever. "
This is usually my problem too arabella.Overthinking.I've learned to just let it go and say "f it".

I've also found that people don't harbor any ill feelings for long.I harbored them much longer than anyone else ever did,towards myself.
Speak your mind,give em hell,and let the chips fall where they may.I was at a party yesterday with some of the same people there.They were all laughing at how the guy was too scared to show up.
Then I found out that he made some very inappropriate comments to some pre teen girls(we're all 30
s to 40's).He has a history of pissing people off.He needed to be taken down a notch or two.
I'm a little intimidating to some,so I have to make a concious effort to be nice.Once I break the ice,I play well with others.