I have ocd, and have an obsessive worry about going crazy. I am taking sertraline 75mg, and it helps some. What should I do to eliminate that worry?

Combined treatment. Not knowing your complete history I suggest combined pharmacotherapy and psychotherapy - cognitive behavioral therapy or exposure based therapy. if you are able to make this work seek a reputable therapist with experience treating OCD. Some evidence that medication reduces symptoms to allow therapy to be more effective. Skills learned in therapy are important for long term management. Be well.
OCD. Please also see a Psychologist expert in anxiety disorders, especially if you have any trauma history. OCD may have a strong genetic piece so the right med and dose can be amazing. But therapy may also be extremely helpful in reducing the stress that feeds into OCD and can aggravate it. We can help--please reach out.