sorry I have to repost this because I need help asap, thanks

"hey, so i have a 96-00 civic with a gsr rear disc conversion. I hate to even post a thread about this but Im in the process of changing the pads and im trying to get the caliper back on over the new pads.. I know the piston is out too far and i know you have to rotate it back in to get more room. But it feels like the piston is stuck out and i can't spin it anymore. I was told that there might be a locking mechanism that will keep the piston from spinning.. Anyone know what im suppoed to do??? hellp i need to get to work tomorrow =/ thanks "