Alrighty...thanks. Now for the advice...
He's probably a baby from earlier this year. A PetCo purchase probably wasn't the best idea, but I can't say too much against them, as I do have a PetCo corn myself (I got really lucky with him though, he has always eaten like a champ).
Your husbandry seems fine, but because he is such a little guy, I would actually think about getting him a smaller tank until he's a bit older.
How much are you getting him out? Did you give him time to settle in after you got him? It sounds like he's probably stressed, which would cause the unwillingness to eat. At that size, I rarely get my babies out, only to feed/clean/water. Once they are well established eaters, generally over 30 grams or so, then I start 'socializing' them and getting them out once or twice a week. It doesn't seem to affect their 'personalities' by not handling when they are really young. 95% of corns are very sweet by nature, that extra few months of minimal handling doesn't appear to change that.
My next suggestion would be to get a day old live pinkie and try that. I've only ever had one young snake (also about 12 grams) refuse a live pink (and she was an on-again-off-again feeder...huge pain in the butt!!). After that, they generally will take a frozen/thawed pink the next feeding.