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.