You might want to provide a little more detail - like what were the other bikes? Do all of the other riders weigh about the same as you do?
Provided you don't outweigh your friends by 30 pounds.
A couple of things come to mind...
1. You might be running a little lean - maybe your float level is low, etc.
2. If you have an older gasgas - they have a composite water pump impeller that can "decompose" and lose its effectiveness. LT-Racing makes a high volume metal impeller.
3. If you were riding with KTMs, they come with a higher pressure radiator cap.
4. Fuel mileage can vary 20% from rider to rider - you may have been more aggressive than your friends.
5. Are you running radiator guards that obstruct airflow through the radiators?
6. Maybe your water level was high to start off with - do you have an EC with the expansion tank?
jeff