Welcome to the wonderful world of kit building, where the kits manage to get everything almost right, but not quite. However the routs do fit the supplied kit parts (normally), and they aren't officially licensed body copies, for which you'd pay a lot more.

The price you pay for this is having to do a bit more more work if you do decide to upgrade. This gives you a chance to shine in the face of adversity and show your true 'can-do' character.

A Dremel is one of your best kit-building friends, and a sanding drum on a Dremel will make fast work of widening out the control cavity. Obviously mark-out the outline of the control plate first, then draw a line a bit inside that to still give a lip to the cavity for the plate to rest on with no gaps showing. You can also draw round the pot so you only remove just enough, and no more.