I don't think countersinking is bad in this case. I did the same thing early on during the Vertical Stab build. I called Vans and they said use 426's and build on. What would concerns me, is by both sides, do you mean right and left or top and bottom sides, of part F-01457-L? If it's top and bottom I would order a new part. If right and left I would build on, after a call to Vans.