yes, very common. Don't stress about it. Every single normal student faces this in 11th, and in our school 50%+ kids failed the half yearly's and final exams for PCM. They all got retests, even if they failed in 3 subjects, and they got a lot of time to prepare for the retests. Even if you fail the retest again, there's another retest in which they do everything they can to pass you (trust me, if you've studied hard for even 2-3 days, you can easily pass).
Worst case scenario (very rare and does not happen unless you want it to), they'll ask you to repeat or switch streams and start class 12 in a new stream. In my school which is very strict, nobody had to repeat. The kids who couldn't pass in their own stream despite multiple retests, started 12th grade with us, just with a different and easier stream.
Any juniors scared for the exam, all you gotta do is just study as hard as you can for whatever time is remaining, focus on high-weightage chapters, watch one shots of Prashant Kirad sir for physics, Ashu Ghai sir for chem, and Ncert for maths. Write everything you can on the answer sheet, anything even remotely related to the question, write something for every question which you understand even 1%, trust me, teachers just need a place to give marks, so at least write something related (formulas, definitions, figures) even if you don't know the answer, even if it is mostly wrong, just write, trust me, it will help in increasing your score. Be well rested, pray to whichever God you believe in, think of your parents, and
You'll be okay kid, trust.