If your border molding is done correctly, your complete denture should fit perfectly. Most of the time, any issues come from the lab. As a certified dental technician (CDT), I noticed that my working models were coming back from the lab with the articulator mounting plates still attached. It turned out the lab was duplicating the models, which led to an improper fit for my CD. Once I started processing my own CDs, the problem was resolved. Pay close attention to this detail. As for removable partial dentures, it's crucial to understand the design and properly prepare the rests. Don't hesitate to ask your prosthodontics professors for guidance.