Don't be too hard on yourself. It's probably not as bad as you think. Many times we make mistakes in building. Just don't crack a canopy! And don't ask me how I know this!
Option #1 - Replace the F-712 bulkhead with a new one and remount the V/S and F-712E tiedown bar. This would probably take a half of a day to drill out, prep, and reinstall. Use the existing hole pattern in the V/S and F-712E to match to the new F-712 bulkhead.
Option #2 - Bolt it together as is and add another set of bolts just above the bottom (misdrilled) row. These would be just below the lower Rudder Hinge bracket. I believe that there is a couple of rivet holes there (see DWG 27A) that you could substitute bolts.
Hope this helps! Let me know if you need additional help.
Vans Aircraft Inc.
I think Joe has just recently started at Van's. Let me be the first to go on the record and say, I like him. A lot. He obviously has empathy for the builder.
So, then, which solution would you do? I'm inclined to go with #1. You?