Do you think I'm being very stubborn about a school project?
Why do you think you're being stubborn about the project?
My group members want to finish it early and I want to wait until the last minute to complete my part.
I know you feel like you can be independent, but when working with a group you need to follow the group's wishes. Completing your part and getting the assignment done is important. You need to work well with others and consider their needs, it's not all about you.
But I don't have time to do it right now. I have other things going on.
I understand that you have a lot of things going on, but it's important for you to finish your part on time. Your group members are counting on you to get it done, so making them wait is pretty rude.