Thank you for applying to the University of California San Diego. We are requesting some additional information from you to complete the review of your application.
Does it mean am I a borderline student or is it just a standard email for all UCSD applicants?
What additional information are they asking for from you? Up to 15% of the UC applicants for each school can be asked for a supplemental/augmented review. No it does not automatically mean you are borderline. It could mean you mentioned a special skill/talent, a disability or hardship in one of your essays.
It asks me to give them fall semester grades and answer one question pertaining to challenges below:
Are there any personal circumstances such as employment, family responsibilities or illness that have significantly hampered your ability to achieve academically thus far? How do you feel these circumstances have prepared you to overcome any personal challenges that might occur while at UCSD?
So did you mention any hardships that could have impacted your grades? If so, then you need to elaborate on the circumstances and send in your Senior Fall semester grades with your answer.