This is a common occurrence especially recently when everything is growing. I don't know how to calm this feeling even though I earned a few percent on the project. For example, I sold UNI for $ 2. I will always remember this and this wound will never heal.
Once you finished the trading, don't look back and check for the price. You need to move on, otherwise, you will get crazy thinking that what you should have done. As long as you made profit, just be happy that you are on the positive side. Thinking that you should have sold at a different time will not help you calm down your feeling of regret. We will always have that feeling but one thing to move on is just look for other opportunities and not go back again and again to your old asset.
I think that feeling is the same feeling as greed and he's already using emotions in trading which is not good. Most traders are like that and did end up regretting because they sold early. I think it's just normal because all you want is to gain profit but you didn't expect it to fold more than what you have expected.
That's why TA is somehow effective if you really want to get close of the price as much as you can.
Anyway, if your target is just to gain profit why regret though? You haven't done wrong with it and I think if you feel the same way again then always think that when you are about to dump be sure that you won't look back anymore.