ORIGINAL: bubbagates
Nervous after any repair is normal. Considering the way you repaired it it's most likely a little over-engineered anyway which is not a bad thing. Take it easy do a few full power runs while having someone hold the plane. Fly it and take it easy and after a few minutes you will relax and will be flying it like you used too.
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If he knows someone with a table saw, or has access to one, rip some 1/2" and 1/4" triangle stock from a piece of light pine (any 2x4). If you can, sneak into the compartment behind the firewall and epoxy some pieces of this triangle stock at the point where the firewall joins the sides of the fuselage.
Anyone flying any ARF should do this if possible. Even little 1/2" long pieces placed randomly in spots will contribute a lot of strength to the firewall area. The manufacturer's hotmelt glue just doesn't hold up.