workload/ competitive nature of imsa

i have a question. I just got accepted into imsa, however, i didnt submit my sat scores and all. i was a well rounded student in acdemics with loads of ecs and awards, however, i am not a bright student. ive been maintaining all a's throughout years in honors and aps but i dont think that enough for imsa. I understand the lifestyle in there is fun but generally, how hard is the workload and how competitive is it? how many hours of hw would you get, is it manageable? currently, i am not used to heavy workload and am worried if i cannot maintain the pressure and skill level of all the other students. one disadvantage i have is i only finished hons geometry and not hon alg 2 trig for imsa, im not sure if that will put me behind.

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also, are all students extremely smart and competitive, because i hope for a learning enviroment where you can relate to and people bring you up when grades are low

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any knowledge about placement exams and how that would go?