Try running a buffer over it,it will look like day one!
Perhaps to an extent that no one will ever really realize.Done properly I.E. primed well and given a couple good coats of finish this wont be a problem.
No,if you do that and buff it it will be gloss!! That is the biggest problem with flat paint:if you dont get it right after spraying then you are screwed since you cant buff it without losing the flatness.On a small scale what makes flat flat is the fact that it is slightly textured,if you flatten it out you have defeated the purpose.
And just remember,Rustoleum is an alkyd enamel,essentially what cars were painted with back in the day - only probably better.Do it and do it right,you will be happy in the end and you wont have to pay a body shop like $6000 for something thats in the end worth about $100 more in actual function.And no im not just talking out my rear,i used to be a body guy who spent days applying PPG worth hundreds per gallon,and now im here telling you to go to the hardware store for paint lol.