Do not ever de-arch or flatten to do an in place center turn, especially when doing a 360 or a 540. Keep a comfortable arch and make sure to keep your hips/pelvis pressed square to the relative wind throughout the turn. Even if you are doing everything else right with your arms and legs, tucking the hip when dropping a knee which and/or pitching the hips with the dropped knee will cause you to move. Another common mistake is head switching too early. Try a "late" head switch to correct this and make sure to keep your shoulders square (don't let your head cause your shoulders to pitch). Finally, I highly recommend getting with a NSL Tunnel Coach or a Skydive University Coach and working on it in the tunnel. DeLand is the best place to go for both of these. Check out www.skyleague.com for the most cost effective tunnel camps out there.
