I’m so scared I’m gonna be a failure as an adult, how do I cope?

well, with your kind permission, I humbly guess  you're  young enough to be my son/ daughter- to begin with.

 if so, you're at the utmost age of flourishing in every way on one hand and a difficult age, too, on the other hand

An old adage, if at first you don’t succeed, try, try, again is a good motto to keep in mind.

Get a fleshlight

Just don't sweat it. Lol. I'm getting old, and I am STILL growing up! Just do the best you can. Be the best you can be. All that good stuff.

I will let you in on a secret - we all feel that way. The difference is, some of us don't let it show. Be as nervous as you want on the inside, you don't need to be confident, just look it. Ninety-eight percent of the time, nobody can tell the difference.

Put your faith in the Lord Jesus Christ and He will make straight your path.  I don't know how many times Jesus said in the Bible "Do not fear."  Being scared of anything is fear and fear causes torment.  You can walk in God's strength and face any problem in life.

you're already a failure

Take one day at a time. You put so much pressure on yourself!!! Let it go!!

You don't know what gonna happen in 5/10/20 years. No one knows and no one can give you any guarantees... you just live your life, make your decision (something wrong one, and everyone makes mistakes, so no need to get too upset about them), you follow your heart and your passions...

The only thing you can do is to do whatever you can today )) try to be a better person compared to the version you were yesterday (but don't overdo it ))) and don't be too hard on yourself ))))

It's gonna be Okay )) and a lot of things are in your hands!!! so don't transfer your personal responsibility for your life on someone/something else.

Stop thinking like you're doing - you're making catastrophe predictions. Truth is, what we believe in this life, we make TRUE.  So if you believe you're a failure, than that's what will happen.

There is a lot of info online (and esp YouTube) about manifesting what we want in life. And guess what? It works.  

Work part time at a grocery store or restaurant and invest in crypto. Don't go to college and go to into debt only to be unable to find a job relating to your degree.