I agree with Uedasan. Not fitting can go either way>>きつい(tight) orゆるい (loose) In addition to your translation このジャケットはとても大きいです, you can say このジャケットは大きすぎます。 Here,「すぎる」indicates the excessiveness of whatever adjective you're using. とてもjust means "very" whilst saying すぎるwould indicate that it is too much of something (in this case, being big). Good luck!

"ジアケット" should be "ジャケット" ／”Doesn't fit” does not necessarily mean "きつい". It can be "loose", which is usually translated as "ゆるい" or "だぶだぶ".