His position is understandable considering what happened with his last marriage.
He probably has a lawyer who is on retainment for all his business and personal legal matters that is bound to look after his best interest. The lawyer is probably making big bucks, and wants to keep this position.
So he isn't thinking about your concerns at all. Prenups don't necessarily have to be bad if your boyfriend is thinking about your needs also. Does it provide for you in the event of a problem marriage, or his business? [ Yes, I know 20 year old's don't let negative thoughts come into their minds when in love] Because of a hard lesson learned it has come into your boyfriends mind.
Not sure if you can reverse all that you have done, but I can tell you that the decision to do it should have come after you found all this information out. You said yourself that you know nothing of the business world so at the very least you should ask for a copy of this prenup to read, and maybe get a lawyer of your own to explain what you don't understand.
If this boyfriend feels the same about you as you do about him, it shouldn't be a problem. If it is a problem, better know now than later.
Probably not what you wanted to hear but..........food for thought
I really hope everything works out for you. Good luck.