belt broken, replaced, now new belt keeps slipping off the drum wheel?

Indesit WG1130T washing machine; the belt broke and i replaced it myself with the proper part; now the new belt slips off the wheel within seconds of rotating; the wheel is not running true; the top of the wheel is very close to the drum, whilst the bottom is far out; i believe this is throwing the belt off; the wheel is fully tightened to the drum; is a bearing on the drum worn out? what can i do to fix the problem? please help!