I actually did set it up as new
Did a quick reboot let see what happens.
If you really want to be sure, wipe it one more time, and set it up as new again, but install only the essential apps that you must have.
If it still reboots by itself, then you have to take a trip to Apple Store, or call Apple Support. Explain to them what you did, and they should swap it out right away (providing that they have stock). If you are within the return period, I suggest refund and re-buy.
I got this phone thru Verizon device payment wonder if I can return it without being charged any fees.