Are you sure you have actual PETG and not another PET type (there are many different types of PET, PET-G is most suited for 3D printing) ?

I have printed a lot with 6+ colors (colorless, black, red, blue, green, yellow, translucent red etc) of PETG with exellent bonding. The parts are super-strong. The only problem I have is that it is virtually impossible to print supports in PETG as they are a PITA to remove as the bonding is so strong.

My settings are Flashforge Creator Dual, 225-230 C nozzle, 80 C bed (3Dlac spray on glass), 0.25 layer height, sliced with Simplify3D using slightly adjusted ABS settings (and without raft or other supports).