I've been studying French for a long time and I've never heard anyone use 'juste' for 'tight' ?! Is this right?!
Yes, it is. Very specific to clothing though. If somehing you wear is too short, or too tight, you say "C'est trop juste".
"My jacket is too tight," is apparently an incorrect answer; I think it is fine.
a jacket is rather a top, like a short coat (in French: une veste, un blouson)
Plenty of people use "jacket" and "coat" interchangeably where I'm from.
Tight is an adverb?
"Tight" is an adjective used to describe the noun. If it were an adverb then it would be something like "tightly" i.e. "my jacket fits tightly" where tightly modifies the verb "fits".
Right, but i am guessing @nidowardana asked that because this is a lesson about adverbs, not adjectives. So is this a case where it is an adjective in English but an adverb in French?
"juste" is an adjective if it modifies a noun and an adverb if it modifies a verb:
What about the word "etroit" for tight? I've used that term in clothing stores in France.
"mon manteau est trop étroit" is indeed accepted.
please define to vs too