Looking for input/advice

Not sure if this is more r/sex or fitness, but; To my fellow skinny, unhung members here (no pun intended) with flat butts, is there really any use in going to a gym? I dont want to put in all that effort to find out I can't have the ass I've always wanted, or that my dick might not be up to snuff. If there's anyone else who's been in this predicament before, any light you could shed would be great ly appreciated.