Wow, okay! Yes, your assumption is probably the reason, smaller internal tube if you repaired the catastrophic piece, especially on the inside. Unless you have not sanded very well or more to increase the internal diameter of the mast step, not sure how to improve your situation without saying to replace the tube. You have to bore it out, basically. And I would assume you wouldn't need more than a couple mm. A suggestion would be to buy a metal disk for the bottom of the step to see if it actually fits in the tube all the way down. They might be magnetic (can't find mine at the moment to test), and if so use a telescoping magnet (Harbor Freight sells them to retrieve bolts/nuts in engine bays) and by sliding that disk down the tube, you should be able to tell where you need to fair it. And, hopefully, your tube is straight from top to bottom.
If you reinforced the tube to the hull, and all around the wooden puck as others have done and posted here, I would not worry about another failure. I would worry about the mast not rotating as it was designed to do, before you sail, just in case. Light air, probably not so much.