Am I a failure?

Yesterday, I really hope that 29th Feb will be a sweet day for me.
Considering the fact that I will only meet the date in another four years make me feel more excited.

However, after I finished marking and key-in my students' marks, every bright colour turn to grey.
Out of 21 students in the class, only 6 students passed.
And now, I feel like I am a total failure, a bad teacher, a loser!
This is not about being dramatic or what so ever, I just feel down as 15 of them failed my paper!
What have I done wrong?
I've tried my best to help the kids and the result seemed like nothing change.
I put a lot of effort this semester. Unfortunately, my effort is worthless.

Am I a BAD teacher?
Bad teacher!
Bad teacher!
Gosh! I really feel bad....
This is terrible.
This is a disaster.