I'm not sure how different roller hockey is from ice (since i only did roller on the street informally with friends). By agressive do you mean checking a lot and hard, or just being stupid and shoving the stick into your back, etc...
Getting hit is part of the game. Learn to take the blows and try to deal some of the blow back. They can hit you to the point where they knock you down, as long as they remember how much it hurt them to do so.
Use your teammates, they are invaluable. Tkachuk scored FOUR goals vs russia, yet they were all assisted by modano, and though tkachuk is getting a lot of praise, people arn't forgetting about modano (who is considered by many to be the best player for team USA right now). Whether you are the guy scoring, or setting the other guy up, the team play dynamic is impossible to overstress.
Not sure what to say, other than stay in physical shape (and constantly get stronger/faster), don't let any one facet of your game slip. Just cause you play defense don't let your shooting slip, just cause you're a center, don't let your defence turn to poo, etc. And get to know your team on and off the ice. Best of luck, i loved playing hockey, though a busted knee and broken leg ended that fun very early for me. Though i didn't really offer helpful advice just wanted to chime in
