There's no genie and there's no such thing as a time machine, what happened to you happens to every investor not only Cryptocurrency investors, there's no room for regret in investing, true investors always move forward and always look for new opportunities.
There's endless potential and possibility in the Cryptocurrency market forget your losses and just look for those opportunities there's no use crying in spilled milk.
That's too easy to say! Everybody has already done some bad trades and you will always keep remembering them. I sold most of my DOGE when it was way under 0.01$ as I never imagined it could ever reach 0.01$ or higher. Till date, I am still kicking myself but it is what it is. Right now, I just try to take profit where I can and always on the lookout for a good opportunity to do some trades.