You'd be surprised. Working out will improve your physical appearance regardless of how good you look now. And that is assuming you are assessing your body accurately. It will also make your face more appealing. It will make your skin have a glow, and guys WILL pick up on the fact that you're in shape. There IS a major difference between a girl with a decent body and a girl with a decent body who gets herself into better shape.
Additionally, working out will help you feel better about yourself. You seem to feel quite badly about yourself and working out is one of the best ways to build confidence in your appearance and in general.
I bet if you were walking around confident, smiling, fit, bouncy, energized, etc., guys would find you much more attractive than if you are droopy, depressed, and giving off a "I feel hideous" vibe. Nothing will change unless something changes.