Education involves a series of challenges requiring students to confront them, expanding their horizons and understanding of the material at hand. These transitions are indeed difficult and they (like most challenges in life) require persistence and often a struggle for students to overcome them. Science and mathematics in particular require rigor and involve objective elements and standards for achievement ( there are clear right answers, and the rest are all wrong) The challenges your teacher presents are likely an important elements in education and your personal development. Your Teacher sounds to me like one who understands all this, and is challenging you engage and grow.
Life is full of such challenges, and the one you face now is an opportunity for you to learn for yourself how to deal with them. Your choice here is to accept the challenge and learn from it, or to evade it and thereby learn to rely on excuses. I believe the latter course will serve you poorly, now and in the future.
The job of teachers and coaches is to inspire students and athletes to do their best, struggle to expand their abilities, and meet challenging goals.
It's your choice, and the consequences for you of the choice you make may have lasting effects.