Sometimes things are just hard and it should be expected that nobody masters it in any arbitrary period (e.g., the course of a two week period covering a topic, or even over a semester).
If you can’t cover the courses materials in a semester then split the course into multiple different classes. Most collages have 2 or more Calculus courses, but you can also pull various aspects of multiple classes into a single introductory one.
If this is the case, then the course should be broken down into a bit that can be mastered in the timeframe allotted.
Then don’t teach a semester-long course about it. Break it up over two semesters