why are my brakes not as good as before i changed them?

i had problems with my vauxhall vectra 08 rear pad change. i couldn't get the piston back, thinkin it had seized i released the bleed point and let a thimble full of fluid out whilst trying to pull the piston back. no joy,so i pressed the brake peddel and it moved in even more! now i was in a worse situation, until a friend told me about this site. i got the pads changed but the peddle travels a long way and is not as responsive