If I come up short you'll probably help me.
→   만약 모자랄경우 도와주세요.

[예문]
A:What are you going to do with money?
  이돈가지고 뭘할꺼니?

B:I'm going to save most of it.
   거의다 저금할꺼예요.

A:Are you saving up for something?
  모으고 있는 이유가 뭐니?

B:Yes. I am saving up for collage.
   대학가는걸 위해서요.

A:How much have you saved?
 얼마나 모았는데?

B:Ninety-three dollars.
   93달러요.

A:That's a good start but you've got a ways to go.
  시작이 좋다만 갈길이 멀었구나.

B:I know it's not much but if I come up stort you'll probably help me.
  얼마안되는건 알지만 모자랄경우 도와주실거죠?

* put (something) away. :~을 저축해두다.
*save up for (something) : ~를 위해 특별히 저축해두다.
*(one) has got a ways to go : 갈길이 멀다.