ceiling fan light pull chain

This is sort of a continuation to an earlier post regarding a project Im working on. I added a pull string light to my pantry and planned on tapping into a downstairs receptacle for power. I just ran the wire through the walls to the crawlspace and hooked up the wiring to the light. Only I just noticed something that I'm not completely sure of and I need some help. The wire that the clerk at Home Depot said I should buy for the new light was 14/2. Only, I just noticed that the receptacle that I need to tap is connected with #12 wire and is controlled at the breaker by a 20amp switch. So, does this mean that the wire I bought and ran needs to be taken out and replaced with #12? Final point of confusion, the outlet I am tapping into says its a 15 amp. What gives? If anyone can help I would greatly appreciate it. I'm at a stand still and would like to get everything working and clean up before the wife gets home. ;) bubba

Light does not work no power, but if you touch the tester to the ground wire and black line it works. What could be the problem? This in the ceiling light not the switch. Thank You.