Looks like your header is all the way in to the muffler.
You will want to have at least 1/8" space between the muffler and header because of the vibration. I will try to take a picture and post here.

Start the CG around 205mm. 200 is ok too. Just don't go any shorter than 200mm for the maiden flight.

I've never had any retract failure so far. Also, exhause exiting to the side looks ugly and more clean up will be necessary.

Don't use any fuel with less than 20% nitro. 15% will not run the motor well when it is in-cowl installation and inverted.