“我差一題就達到六十分了”的英文?

I am one question shy of 60 points.

..The past perfect tense denotes that the first action which took place before another action in the past(before/after)
eg:-By doing one more question, I had reached 60 marks.
eg:-By working one more question, I had reached my 60 marks.
eg:-It is one more question I did "before" I got 60 marks.
eg:-I had reached 60 marks "after" I did 1 more question
eg:-I am one question shy畏豫的膽怯的冇做那一题目 of 60 marks..
eg:-I am one question short of getting 60 marks.
eg:-I need to get one more question(right or added) to have reached 60 marks
eg:-I have to write one more question to get 60 marks..

Alan的答案已不錯
另一種寫法是
I'm one question short of getting 60 points.

或較"正面"的寫法亦可以表達
I needed to get one more question right to having 60 points.
If I'd have gotten one more question correct to reaching 60 points. 
當然這些很長氣卻包含"感情"回憶。