YOU SAID:

i should go get my keys, i forgot them inside

INTO JAPANESE

私は私の鍵を取りに行くべきです、私は中にそれらを忘れました

BACK INTO ENGLISH

I ought to go get my key, I forgot them inside

INTO JAPANESE

私は自分の鍵を取りに行かなければならない

BACK INTO ENGLISH

I have to go get my own key

INTO JAPANESE

私は自分の鍵を入手しに行かなければならない

BACK INTO ENGLISH

I have to go get my own key