Hello.
I suspect most of your trouble boils down to tuning your PID coefficients. Some of the turns on your course look challenging, particularly the sharp turns. It will likely be difficult to tune your robot to reliably complete those turns with only a proportional term. The derivative term is typically very important for stability when tuning a line follower, especially at higher speeds. I suggest reading through Ben’s posts in this thread about PID tuning; there is a lot of good information there you might find helpful.
Brandon