When you are drawing your opening hand, either before or after a mulligan, drawing too many cards is not considered to be drawing extra cards as long as it is noticed and taken care of right away. Errors like this are fairly common, they are also easily caught and correctable. The technical name for this infraction is Improper Draw at Start of Game. The penalty is a warning, and the fix is to take two cards from that hand and shuffle them back into the library. This player can then choose to either keep this hand or continue to mullligan. While the ‘forced mulligan’ is not the best thing in the world, it is better than receiving a game loss for drawing extra cards. If this error is not noticed and dealt with right away, the infraction is drawing extra cards and the penalty is a game loss. So it is in your best interest to call a judge right away when you do this.

Finally, if you do draw too many cards, notice it and do not call a judge, that’s yet another penalty which will get you DQed.