1) IF I do nothing, am I going to have trouble the next when I return.
-Possible, if you have been warnned by CBP.
2) Can I apply for RP?
-Sure.
3) When I apply for RP, can I use "working" as the reason for staying in China (not an expat position). The custom seemed to have problem with this reason. They suggest that if I return to China and work there, I should just give up my GC.
-If this company owner is US resident, it is OK. Oherwise, you may find some different excuses such as stay with your parents, job cooperation with the Chinese company, cooperation on research with a Chinese school, etc.