Nice print! I also own the Stainless Steel Apple Watch as well as the Sport and have not had any issues installing the charger for either. However, I've only printed this in PLA. The charger diameter is the same for both models however, the thickness is different .30" for the Sport and .25" for the SS.
Sport: 2.08" (52.83 mm) diameter and 0.30" (7.62 mm) thickness.
Stainless: 2.08" (52.83 mm) diameter and 0.25" (6.35 mm) thickness.