Yes, you have to turn off the Inifinte Ammo cheat. The more you press it, the more it adds into your inventory. Once disabled, it stops and you can proceed further. No need to restart the checkpoint.
How do so many people have the game early? Mine is still on pre-order status.
as pwiz already stated:
close origin-> change date to 5th February(or 8th in EU) -> disable internet connection-> start the game - > game will ask to provide origin log and pass -> enable internet -> type log and pass -> play game.
Warning though, everytime i disable my connection, its takes a lot of faffing to get it back again, my ip address seems to dissappear, and wont come back, i have to reset my router every time, then run through a few trouble shooters, and doing this everytime i want to play the game is pretty crappy.