I’m lack of 13 points to pass

[flytothesky]

Hello~ Can you help me say this naturally please?


A: Oh, no..
ⓐI’m lack of 13 points to pass this subject.
Do you think teacher will do me a favor? If I beg him?

B: Well, it’s 13 points, not 3 points man.
ⓐBut anyway why don't you give a shot?

[Tdol]

1 I'm 13 points short of the passmark.

2 It's OK, but I'd be tempted to get rid of 'but'.