One technique a beginner can use when opening up the holes in a spinner is fairly easy to do right.

Use an exacto and take say two cuts out of one hole. Then go to the other hole and take an identical two cuts. Test fit. Repeat.

Another technique that works is to make a template for the hole shape you think will work. Transfer it to both holes. Make sure it's the same on both sides. Measure to be sure. Then trim both sides to the marks. Obviously, you won't need to do the 2cuts/side deal. But if the new holes aren't big enough, you can then do the two cuts/side deal.

Actually, you don't have to be a beginner to do either.