Failed to file 2020 taxes with capital gain in stocks

I failed to file my taxes of 2020 and I forgot that I had $20,000 capital gain in employee stocks that I sold that year. Both state (Oklahoma) and Federal.

My main concern is jail time. I'm not sure how to determine what warrants jail time or doesn't. Should this be a concern or are the fines/penalty payments the only things I need to focus on?

edit -- I've already taken care of this, but knowing that jail time isn't something that I need to worry about would be a relief. I'm new to taxes and stocks.