YOU SAID:

I think I will fail my quiz

INTO JAPANESE

私はテストに落ちると思う

BACK INTO ENGLISH

I think I will fail the test

INTO JAPANESE

私はテストに失敗すると思います

BACK INTO ENGLISH

I think the test will fail

INTO JAPANESE

テストは失敗すると思う

BACK INTO ENGLISH

I think the test will fail