Brake pads changed, but what did I do wrong???

Hi, the search function did not reveal anything that was already before … I changed my pads on Saturday with the help of the book “So wird’s es” . But I believe I did something wrong … Only don’t know what …. To the value path: wheel down, with 6 hexagons the 2 screws loosed and the brake caliper removed … disc measured (was still ok and also without bars) and then it started with raining *kotz* I therefore only checked the smoothness of the sleeve in the brake caliper, this however nic it was cleaned with a bottle brush as in the book. It seemed to me that it was not necessary, it was very easy … everything was cleaned and put together according to the instructions. In itself everything was without problems. To this day I drove about 50 km, but had this feeling that it did not brake as well as before the “repair”. So I operated the brake pedal very easily with the left foot and gave it gas at the same time. Result it was to feel that the coverings were not smooth h “have let go of the disc”, so they still cut on it. After ner 1 sec there was nothing more to feel when accelerating … So I looked if the disc started biting, because this “permanent” grinding on the disc is certainly not in the sense of the inventor and see since the disc got easy e occasion colors … What I don’t understand is this cleaning of the “bust” really so evocative, also did I feel it would be smooth??? It certainly isn’t true, because he could be pushed in without any problems … Since I certainly need a brake system for my conscience, I would now repeat the whole mess again, just this time with new windows. Was with Pitstop and they wanted to make for 210 Euro (ats disk + coverings) , a lot of wood … Therefore the question are the “Set ́s” offered at E-bay for 60 Euro or are these under no circumstances to be recommended??? But if they are for my Polo (60 HP SDi Bj 98) v on the reliability are ok, what did I make flat the first time??? Thanks for the answers. Greetings Naik Polo 1.7 SDI Bj 98