I also got accepted in UCSB and I emailed there admissions about my D and they told me “Thank you for notifying us of your low grade in Pre-Calculus. Your application and senior year grades have been reviewed. Given your strong academic history, we are able to waive your low grade in Pre-Calculus as long as you complete the rest of your courses with grades of C or better. Please know that any additional grade below a C could negatively affect your admission status in the future. If you do receive a grade lower than a C in any other course, please notify us immediately”. So hopefully Ucla does the same