3 friends. 1 graduation party. Can you help?

My 2 friends and I are all planning our high school graduation party. Originally our moms were going to make it a surprise party for us, and then they realized that it might be fun for us all to plan it together. It is going to be at my friend Katie's house, and Kate's mom was the one who originally had the idea, so Katie is the one taking control. We only started discussing it yesterday (and only through texts) and instead of the 3 of us together, it was Katie going between me and my other friend, Grace. I just feel like Katie is going to have the final say, and either Grace or I is going to be left out at some point. Katie thinks I'm worrying for no big deal, but none of us are going to prom and none of us had a big sweet sixteen or anything, so this is kind of the big party we've been waiting for, and I want it to be how all of us are envisioning it. Katie had one idea for a theme, and I said yes and then I took it back, and now I think she might be disappointed! I just want this to be a really great experience (in both the planning and the actual party) and I was wondering if anyone had advice on how to do so. I want us to all plan it together and spend time together in the process instead of us just texting each other with guest lists and theme ideas, and then having Katie and her mom actually execute it. Plus Katie and Grace have been spending a long time planning Grace's sisters wedding (they are both bridesmaids) and I kind of want the chance to plan something myself now. Any advice appreciated!!