As always, thanks for the advice guys and gals. Much appreciated.
I was VERY fortunate that I hadn't drilled the countersink holes deep enough. This gave me the option to repair the irregular holes by drilling them deeper to the correct diameter.
Based on the advice from the guys in this forum, and a bit of research from Brad Oliver's website (RV7factory.com) I was able to make myself a pilot hole guide for my countersinking flute.

Here is probably the worst example of an irregular hole. Most of the holes were round and smooth, and the others that were irregular were much less severe than this one.

Using my new pilot guide, I was able to fix this particular hole so that it now looks like this.

It's still not perfect, but it's MUCH better than it was before. I'm still fixing the holes as I'm going very slow and careful. It seems I may have been very lucky in not wrecking my spars. Another lesson learnt in the building journey.
Having an absolute ball!!!
