Poor aim will disqualify you from being cleared for duty with a weapon. If after remedial training, you still can't pass, you will likely get fired. During initial training, you won't pass, and if you don't pass after remedial training, you will be dropped from the program. Example: In the C.F. on BMQ. If you fail to achieve PWQ2 performance objective (its complex to explain, but most pertinent to your query, would be 27/30 rounds in centre of mass, with groupings no larger than 6 inches, from the prone position with a C7A2 service rifle at 300 metres.) If you fail it, you get an intensive crash course from the instructors and a re-shoot. If you fail that, you fail the course and are Returned to unit (reserves) or put on PAT platoon (regular force) in the reserve, the unit decides if they wish to put you back on course (it comes from their budget and ties up a slot with an unqualified solider) if not, you are discharged. In the Regs, you almost always get another chance to re-do the entire course. If you fail it again, again, you are discharged.
If you miss and hit someone in the foot? Well, if they don't go down right away, you keep shooting and trying to hit centre of mass. If they do, you restrain them right away. When questioned about it, you truthfully answer "I attempted to fire for centre of mass, but I missed (or it was the only area of the target which I had firing solution for)"