whenever you do a brake job the brake pedal will always go to the floor because the caliper has to push the piston so the pad is matched up with the rotor. See a brake pad never really leaves contact with the rotor it just rests on it . Just always remember to pupm the brakes after changing pads.
p.s the shop should have done this for you!!! If you were back into something while backing out of a parking space they would have been in deep s**t!