YOU SAID:

I gotta go to school at 9 AM tomorrow.

INTO JAPANESE

私は明日午前9時に学校に行かなければならない。

BACK INTO ENGLISH

I have to go to school tomorrow at 9 am.

INTO JAPANESE

私は明日午前9時に学校に行かなければなりません。

BACK INTO ENGLISH

I have to go to school tomorrow at 9 am.