YOU SAID:

I must say that this is quite boring.

INTO JAPANESE

私はこれはかなり退屈だと言わなければなりません。

BACK INTO ENGLISH

I must say that this is pretty boring.

INTO JAPANESE

私はこれがかなり退屈だと言わなければなりません。

BACK INTO ENGLISH

I have to say that this is pretty boring.

INTO JAPANESE

私はこれはかなり退屈だと言わざるを得ない。

BACK INTO ENGLISH

I have to say that this is pretty boring.