Welcome to RCU. What kit is it? At 95% complete it's a bit late but yes, 3.5 ounces in the tail is a bit much. If you haven't started to cover yet you can move things around or make changes like installing two elevators and the rudder servo in the aft section of the fuse. Most the time they tend to come out tail heavy. During the build I like to tape all the hardware on the outside of the plane to get an idea of where the gear will need to be to get close to the CG before I hard mount anything. I have a hatch in the bottom of my Extra just behind the canopy where I have my three tail feather servos mounted then mounted all the rest of the gear inside the fuse center section to attain the CG. It's an old Goldberg kit. A heavy tail wheel assembly helps a little but at this stage of the build you may just have to add the lead?