Having a posterior placenta with grade 3 maturity at 35 6 weeks is generally considered normal. The location and maturity of the placenta can vary from person to person, and having a posterior placenta is common. Grade 3 maturity indicates that the placenta is functioning well and providing adequate support to the baby. However, if you have any concerns or if your healthcare provider has mentioned any specific issues related to your situation, it's always best to discuss them with your doctor for personalized advice and guidance.