Best way to fix the fuel tank is to drop it in the trash can and produce a new $10 bill to replace it. Don't ever screw around with fuel tanks or hoses, if even the slightest doubt of anything replace them. As far as you plane goes you better suck up the glow fuel with baby powder and cat litter. Otherwise your plane will start to disassemble itself on the inside.

The poor performance came from what was once a small airleak that caused you engine to run lean. Then it got bigger. I doubt that epoxy caused any problems.

First suck up the oil in your plane. Then REPLACE your entire fuel tank AND hoses so that your entire fuel system is brand new. Your talking $10. Then try again.

By the way ... who ever told you to use epoxy to repair a fuel tank should no longer the person you listen to for RC advice. Unless of course ... that person was you.