YOU SAID:

I can do so much better, I'm disappointing in myself.

INTO JAPANESE

私はとても良くできる、自分自身に失望している。

BACK INTO ENGLISH

I can be very good and am disappointed with myself.

INTO JAPANESE

私は非常に良いことができ、自分自身に失望しています。

BACK INTO ENGLISH

I can be very good and am disappointed with myself.