It will be the scariest experience of your life before you go in, and while you are in there it will transform into the most rewarding.
I had gone 15 years before going to confession. I had a lot of soot on my soul, and I shudder today to realize that I was living in a state of mortal sin, separated from God. Had something happened to me during that time… well, I can only praise God for His mercy in keeping me around long enough to bring me back to the confessional.
Honestly, I was shaking before I returned. I had forgotten how to make a good confession. If you go to a good Priest, he will help you along - he will just be glad you came back.
I just heard a guy on the radio say that he came back after a 30 year absence, and before he went back he sat at the computer any typed up the list of his sins. It really opened his eyes. While I didn’t do that, I highly recommend it.
You probably won’t remember everything. That’s OK. If you sincerely confess everything you remember the Sacrament takes care of the shortcomings. You are only obliged to confess a forgotten sin at a later time if you recall an unconfessed mortal sin. I have done that, because after missing for 15 years, I didn’t remember everything.
Finally, the Priest I went to gave me a great piece of advice: once you confess, Satan won’t like that one bit. He will try to keep the guilt of what you did with you, making you doubt that God’s forgiveness can really be so simple. Don’t fall for it. Once you are absolved, your sins are gone! Knowing that made that confession a literal “born-again” experience, as a Protestant may explain it - a weight lifted, a sense of relief and joy. Also, Satan will continue to play upon your weaknesses. This is why it is imperative that you keep going back to get the graces to fight those long-ingrained temptations.
Just do it. If you can’t bring yourself to go to a Priest face to face, or one you know, then go to another behind a screen. Do not let fear or pride keep you from the confessional. You won’t regret it.