If you have to follow the appendix format that your course instructor has given you then there's no harm in many people having the same appendix. It usually happened with me when I had to make lab reports. We were divided into 4 groups and the report is 5-7 pages only. My plagerism peaked at 68 percent. Our instructor was totally fine. Has the other group have the same plagerism percentage? Make sure you email your professor to let him/her know about the situation.
Submit your assignment before anyone else. I always did that and plagerism was much less.
I used to have my group members keep an eye on how's submitting the paper lol. So we submit it like week before deadline haha. Yes turnitin compares it to all the assignments that were submitted.