YOU SAID:

The first person to go to the store was lining a potato

INTO JAPANESE

最初に店に行ったのはじゃがいもを並べていた

BACK INTO ENGLISH

The first thing I went to the store was lining up potatoes

INTO JAPANESE

私が最初に店に行ったのはジャガイモを並べることでした

BACK INTO ENGLISH

The first thing I went to the store was to line up the potatoes

INTO JAPANESE

私が最初に店に行ったのは、ジャガイモを並べることでした

BACK INTO ENGLISH

The first thing I went to the store was to line up the potatoes