Informing my supervisor of discrepancy in the results
In my opinion, it is absolutely essential that you are completely open about this.

If you cannot reproduce his results, at least one (possibly both) of the following are true:


You are doing something wrong. You are a student and he is your supervisor. It's his job to help you if you are doing something wrong. There is nothing to be ashamed of. It's better to be delayed with correct results, than on time with wrong results.
He was doing something wrong. Don't be afraid! You are not accusing him of anything unethical (*). If his previous results or his understanding are genuinely in error, he should be very interested in knowing this, and grateful if you discover such an error.


(*) If you do suspect unethical behaviour, the question is entirely different and better asked separately.