YOU SAID:

I just a eat a potatoe

INTO JAPANESE

私はジャガイモを食べるだけ

BACK INTO ENGLISH

I only eat potatoes

INTO JAPANESE

じゃがいもしか食べない

BACK INTO ENGLISH

I can only eat potatoes

INTO JAPANESE

じゃがいもしか食べられない

BACK INTO ENGLISH

I can only eat potatoes