Yes,you can file the hole to the appropriate dimensions.Make it round if you wish but I would get it that extra centimetre closer.I made a small wood piece with a hole to support the arm from underneath with a Rega arm,experiment here.But if you can fit the arm into the hole,it's maybe not even necessary to do any more.Jean says this is O.K.The extra centimetre or so doesn't really make that much difference to the alignment.