If you can prove that you paid for, like a copy from you bank statement if you paid by check/creditcard/debitcard... you can sue them.
And to be arrested for shoplifting, you have to prove INTENT. Even if you >accidentally< forget to pay for something, meaning you did not attempt to hide the merchandise (under a coat, in your pocket, etc) this does not show intent. So to answer your question, no, you can't, and if everything you stated was true I would file a lawsuit against wal*mart, it wouldn't be the first time someone has done so.
Also, there are several steps to follow when working as a security guard/loss prevention when it comes to catching shoplifters
1) see the person approach the aisle or display
2) select merchandise from shelf (this is done so that you don't accidentally stop someone for having an item on them for comparison purposes, like when a female brings in lipstick to make sure she buys the same color)
3) conceal merchandise with intent to steal
4) maintain eyesight/camera on suspect to ensure suspect does not "ditch" merchandise
5) suspect must leave store without paying
*Also*
Be careful what people tell you on this site, most will say anything to get the 2/10 points.