I don't know you or your sensei, but I would tend to suspect that this has little to do with kata and a lot to do with team work. The world as you will come to experience it will not give you the team you wish to have, nor will it gift each team member with similar capabilities; and yet you will be judged as a team, and you cannot shrug off the failure of a team member as not your fault - team means win or lose it *is* your fault. Teams win or lose together, and the failure of one is the failure of all.
In any team, communication is key, as is having a team leader. This must be discussed and agreed upon. Assigning labels like 'selfish' and 'sloppy' is not going to get you where you need to be; it's immature behavior that is not indicative of a team player or a leader. I say that with the understanding that you are young; this is perfectly normal for someone your age.
However, this is an opportunity to make a better person of yourself. If I may offer a suggestion, it would be to ask your teammates for a time when you can all get together outside of the dojo and talk over how you wish to approach this. Talk about the need to agree on how to do the kata, what speed would be most appropriate to every member, and who should lead the team. Come up with a training plan and stick to it; consider breaking down the kata and doing it step-by-step, a few moves at a time until everyone can do it easily together, then add another few steps, then another, and so on. Be ready to work outside the dojo; don't expect to be given time during training to do it and become proficient at it. Be friendly and open and drop preconceived notions like 'selfish' and 'sloppy' from your own mental processes. Think only in terms of what each member is capable of doing and how the team can best accommodate that. You must sacrifice your own ego to the needs of the team; and this can be difficult; we all have ego, pride, and personal needs. Teamwork means the team comes first and you come second. This, by the way, is also what leadership means.
In the Marine Corps, we often were assigned team goals, including long distance runs. We did not run as individuals, we ran as a team. That meant we ran as fast as the slowest man, and we did what we had to do to make the slowest man faster, such as carrying items from his pack if we had to, offering encouragement and not criticism, and keeping our morale high. The teams that finished first, but with stragglers, lost. The reason for this is that in combat, if you arrive first to the fight, but without the people you need to do the fighting, you lose.
Team means everyone, together. Put aside all thoughts of ego, all thoughts of how others are, and consider the team as if it were a new person, a product of the three of you, and not you personally. What benefits the team? If it doesn't benefit the team, it's not a good idea. Do what makes the team win.
This is the key, in my opinion. Anyone can do good kata given six months. Anyone can do synchronous kata given six months. But only teams think and move together in a way that judges can clearly see. Teams that act as a team and not as a group of similarly-trained individuals stand out.
For examples, watch professional cheerleaders. They each have an ego and of course they think highly of themselves; but not when they are performing a cheer. There is no star in cheerleading; there are only members of the team. Nobody watches so-and-so of the Dallas Cheerleaders. They watch the team as a team.
Being an effective member of a team is a life skill that will serve you well the rest of your life. Take this opportunity to learn what being a team member is all about and grow in maturity. You will be very glad of it later.
