I dont know if this will mellow out or did I screw up?
You didn't screw anything up. There's a world of difference between stuff that got a little bubbly in the fridge on its own, what you get after you allow the yeast to complete the job, and the hard cider you buy in the store. The first has sugar still in it because the yeast isn't done, the second is dry because the yeast ate all the sugar, and the last has been back-sweetened. Three completely different animals.
I wait over a month to move it off its lees (yeast cake) and then let it sit out to the 3 month mark.
I'm not sure how long I let my last batch of cider sit in the secondary, but it did spend a lot of time in the keg. Most of a year. I used ale yeast, added a few pounds LME, and force carbonated it. It never really mellowed and was bone dry. I like a dry wine but this was too much. I'm sure the acidity and tannins didn't help.
I told the guy at my LHBS, and he suggested that next time I add potassium sorbate (interferes with yeast reproduction, available your LHBS) when it's done fermenting, then back-sweeten before carbonating.
Hmmmm. I think I may start a batch while the cider is orchard fresh!