Brake dramas

[Bushbasher]

Just fitted new discs and pads to the wagon (AUII) and now the bloody pedal has gone all spongy and goes to the floor, I'm guessing I have blown a seal out or something while pushing the pistons back into the calipers cos nothing else makes sense. It wasn't till I had finished and bled the brakes that I realised I hadn't taken the top off the master cylinder and removed some of the fluid to make room for the back flow of fluid. So what would most likely be the problem, master cylinder seal or is there a valve somewhere in the system to do with the ABS perhaps that may now be stuck open? I can't let the missus loose with the wagon again till it's sorted cos it don't pull up real well at the moment. Any pointers or clues would be greatly appreciated.

Cheers
Bushbasher