Sounds like you were doing the same thing I was doing, aim low. You said you don't have access to a barricade for practice, that's kind of tough. How about the place where they hold the matches? Can you talk any other members of the IDPA club to let you use their facility, or let you shoot the actual qualifier?
I shoot a Wilson Combat Protector .45 ACP in CDP, a Glock 19 in SSP (also Sharpshooter), a Browning High Power 9mm in ESP (Marksman) and S&W Model 64 .38 special in SSR (Marksman).
Your G21 also let you shoot in CDP division, a G17/9mm would be easier in SSP since you don't have to fight the recoil of the .45 ACP , not that the .45 is uncontrollable. Now if you really want light kicking 9mm, lighter trigger pull and longer sight radius, the G34 would be the gun to get. The G34 is the ideal IDPA game gun. I think I'll borrow someone's G34 one day and see how much better I can shoot with it.