The dimensional differences you’re seeing between the CAD model and printed object may be due to normal material shrinkage when cooled. PETG-HF may be worse than other filaments. I’ve certainly experienced frustration with tight tolerance fits. You’ll have to find ways to compensate by either adjusting the CAD model or tinkering with some of the print settings and options available (e.g.: bed / filament / cabinet temperatures, print speed, surface thickness, infill types, etc.). It takes experimentation.