Why does my 2002 mustang shift so poorly?
A Mustang with a racing clutch is going to feel way different than a Honda Civic. They're two different words (practically on the opposite ends of the spectrum so I'm surprised you wanted it). One is designed to be smooth and comfortable, the other is designed to be fast and aggressive. The racing clutch will tend to grab "all of a sudden" when you let the clutch out so you will feel the shift shock much more. The racing clutch will also be much more intolerant of rpm differences, so make sure you are giving plenty of gas on the upshifts and rev matching on the downshifts. You might have to brush up on your driving/shifting skills to get everything right. Going into reverse takes practice on any given car. Make sure you are at a complete stop and the car is in neutral before going into reverse.
If you still don't like it, you will have to put a regular clutch in or go back to Hondas.