To install new pads I connect a hose to the bleed valve and route it to a container. I then open the bleed valve and push the piston back with my fingers. Makes retracting the piston much easier. (Do the rear fixed calipers one side at a time.) If you don't open the bleed valve all the fluid has to be pushed through the M/C compensating port, which is only about .020" in diameter.

It's not clear what you did "wrong". Pushing the piston back without opening the bleed valve is okay. It just takes more force and there's a chance that the reservoir can overflow.

You're going to have to start bleeding and see if you can get the pedal back.

Make sure you know the dividing line between the front and rear reservoirs so you can read the level. Many let the rear reservoir run dry because they don't know how to read the level. When filling the reservoir it is often necessary to wiggle it back in forth in order for fluid to flow over the dividing baffle and into the rear reservoir.

Duke