Do you know no one, not a single person we normally think of as beautiful think they are, most of them look in the mirror and wonder why anyone can love them with that longer nose, or one breast that is 1 mm larger than another, we laught about it, but to them, they are deathly afriad of it.
You have hidden in shame and never learned to deal with your issues.
So you have some scars, so what, you can not tell from my photo well, but I was in a serious accident 20 years ago or so. I had 100's of stiches on my forehead alone. There are scars there, my arm looks like I was in a knife fight and lost, I lost part of a eye lid, so one eye is much more open than the other.
Guess what unless I mention it, most people don't notice, ( maybe the eye) but no one even asks unless we are close enough friends that they feel they can. No one laughts,
No one laught at the midget in walmart, and god only knows about the 500 pound lady in spandex who perhaps needs to be laughed at for clothing choices.
Adults are accepting of other people, ok, a few may not be, but you move on past them.
The problem now is not the scar on your arm, but the scar on your mind that keeps you afraid to be yourself, you have a arm, I work with people all the time that would love to have a arm,
You merely need to wear what you want, and do what you want, and let others worry about them. If you are afraid of what others will say or do, you will never do anything.
I would suggest some couseling to help you learn to be the best you that is possible and accept yourself just the way you are.
For the actual scars, you can of course consult with a plastic surgon, there are many new things that is possible., or heck get them cover with tattoos, we have a lady we help that looks like a bill board.
The thing is, that the only thng stopping you from doing all those things, is you.