I don't know your enlarger but I am wondering whether the lamp house is focused correctly.
Does your enlarger have a prefocused lamp? If so, that's probably not the problem. Otherwise, check the lamp socket to be sure it is aligned correctly so that it produces even light.
Secondarily, check to be sure the lamp is inserted into the socket correctly. If it doesn't fit right, it won't position the filiament in the focal point of the reflector.
After that, as others say, the lamp you have chosen might not be up to spec.