YOU SAID:

he was mortified and said so.

INTO JAPANESE

彼は悔しくてそう言った。

BACK INTO ENGLISH

He regretted it and said so.

INTO JAPANESE

彼はそれを悔やみ、そう言った。

BACK INTO ENGLISH

He regretted it and said yes.

INTO JAPANESE

彼はそれを後悔し、はいと言った。

BACK INTO ENGLISH

He regretted it and said yes.