I wouldn't lose any sleep over 1/8" gap. Maybe after sitting for a day wired together the panels will be more cooperative though. If they're tight to the forms and you can't find an spot that could be sanded, trimmed or beveled to allow a tighter fit I would move on.

  I will suggest you adjust the thickening agent(s) for your fillets to match the finished color (after epoxied) of your material. The 1/8" of exposed fillet will not be noticable if it matches the color of the material. The darker Sapele option is easy to match but if using Okume you may want to lighten the fillet color a bit. Some tape on the outside before applying the fillets will save you a lot of sanding later...

  HTH

Years ago, when stitch and glue was a new technique, I built a small sailing skiff. One seam at the bow opened to about an inch. I glassed the outside, filled the seam with thickened epoxy, and glassed the inside. Never had a problem with it. -Wes