I have to do a group presentation, and my group has a google PowerPoint that we can all edit and work on at the same time. I opened the PowerPoint today, and someone from my group had already looked up and put in information that I was supposed to do. I didn't get mad or anything since it's OUR project - not just mine. So I just decided to work on other things that no one had done yet. I pretty quickly got group message from someone in my group saying basically "To everyone in the group, please don't add things or change things on my slides because I'll just have to go back and delete whatever I don't think is relevant and that takes way too much time". I didn't even think this person was talking to me, so I kept working on the PowerPoint. Then I got sent a personal message saying basically the same thing, so I knew it was me. I just replied "Ok, sorry about that." and I haven't done anything to any of the slides since then. I felt like she was basically telling me that I can't work on my own project. I mean, I get that it would have been wrong to just completely remove what someone put on a slide, but I didn't do that. I just added a couple of things I thought were important. I thought we were supposed to be helping each other and working on this together, so I didn't see anything wrong with that. After all, I didn't get mad that someone had went ahead and done the work for my slides. If I was in the wrong for trying to help and contribute to my own project, please let me know.
Group message your group and tell them that someone completed your section. It may have been a misunderstanding in which another student thinks that is their section. If so, you'd be able to work on the section they were really supposed to do. I bet that's what happened. Miscommunication.
Communication is key in group work. I don't think you were wrong exactly, but if you had designated topics everyone decided beforehand that they would do, I think you should have said something before you started doing work. Just because you did not get mad doesn't mean other people will react the same. I know it sucks, but sometimes you have to grit your teeth and bare it until the project is over.