YOU SAID:

I am not a going to with a in the monday

INTO JAPANESE

私は月曜日にに行くつもりはない

BACK INTO ENGLISH

I am not going to go on Monday

INTO JAPANESE

月曜日には行かない

BACK INTO ENGLISH

I will not go on Monday.

INTO JAPANESE

月曜日には行きません。

BACK INTO ENGLISH

I will not go on Monday.