Smooth Scroll Navigation needs to be fixed

I posted a job on here looking for a developer to simply add a smooth scroll navigation to a one page html file. The designer failed to complete the project on time so I am having to re-list the project in hope of finding a designer who can pick up the pieces and complete the project. As it stand the the smooth scroll function has been added but it is very very jumpy and this needs to be corrected. If you are 100% capable of editing and correcting html js and css then please bid. This should only be at the tops 2 hours work. I consider all bids.