As you know, your personal contribution to the project can count for up to 100% of your grad. Git keeps track of every single commit you make, and github displays these in nice graphs which you can see by clicking on "Graphs" and then "Contributors", as shown in the images below. By default, these graphs are for the "master" branch, but you can change the chosen branch by going to "Settings" and changing the "Default branch" to whatever you want. Please do this if your main branch is not "master".
Anyway, the Contributors graph tells us exactly how much code you have contributed to this project, and thus is very useful in determining your final grade. If you feel that it somehow missed some of your commits then add hyperlinks to your commits to your Personal Log or add your explanation there. That way, I can't miss them. Note that, if you commit to your personal branch and then merge/rebase into master, your commits will be in master after the merge.
Don't be this guy.