I think the last post from SpecialK sums it up pretty well.
One thing to consider that might help...
Don't worry about whose idea gets used. Look at the long term issue. You need a good demo reel. Can your group agree on something that will fulfill this need? Remember you can always re-use a character or skill to do your own individual work for your own reel.
Don't feel like the group project is everything to your future. No matter how good it is, you will have two other people with the same thing on their demo tape too.
Something I highly recommend to remember: When you estimate time schedules for each task, always multiply by 3. If you think it will take a day, it will take 3. If you estimate a week it will take 3 weeks. This is a good rule even later when you are more efficient with time, because you may actually want a life, and need "buffers" to work in things you didn't account for in your schedule.
You can fight this issue all you want, but the wisest approach is to chose projects that you think you can do easily, but are still effective in showing your skills. If you get done early you have time to work on your own stuff or keep refining your project. If you barely finish, imagine how screwed the other groups are.
What ever you do, sit back relax and calmly figure out a solution. The whole point to working with other people is to be able to get things done when you disagree. If everyone always agreed, employers wouldn't look for this skill. There is also no point in beating your self up for things you can't control. You have to do a group project, so make the best of it.
Talk to your instructor if you can't work it out. They might be able to point out what isn't practical, or perhaps make a command decision and choose something for you.
Hope this helps,
Urp
P.S. Storyboard everything. This is not for the instructor- this is for your own sanity. If you don't account for every element and shot, you will die a slow death.