Original poster : your problem is with the feeding system surely. There is a little plastic part that moves and makes sure only 3 BBs get loaded. This part might lack a spring or might be broken altogether.
1. If possible get a replacementąt Canadian Tire (or where you bought it).
2. If 1. is not possible, find a M3 disassembly tutorial (it's more or less the same) and strip it down to the inner barrels. The part you are interested in it screwed to the inner barrels. Look at it and compare it with what it should look like on an M3.