YOU SAID:

my jumper was worn by a jumper (a person that jumps)

INTO JAPANESE

ジャンパー (ジャンプ人) が私のジャンパーを着用していました

BACK INTO ENGLISH

Wore my jumper jumper (who go)

INTO JAPANESE

(が) 私のジャンパー ジャンパーを着ていた

BACK INTO ENGLISH

Was wearing a jumper jumper (but) I

INTO JAPANESE

(しかし) ジャンパー ジャンパーを着ていた

BACK INTO ENGLISH

(But) was wearing a jumper jumper

INTO JAPANESE

(しかし) ジャンパー ジャンパーを着ていた

BACK INTO ENGLISH

(But) was wearing a jumper jumper