drive belt on Hotpoint WF215?

The belt on my machine has come off. I have managed to get it back on twice but each time the belt moves inward toward the drum plastic shield which then causes the belt to rub and eventually stops turning. Any clues as to why this may be happening? Also I have presumed that the belt goes over the grooves on the motor spindle closest to the motor housing, is this correct?

it is very difficult to work with the belt as the back panel doesnt come off. Have to work via the top and a small aperture at the bottom
Thanks