Help with first football game?

All right, so I'm on the punt return, punt team, kickoff team, and starting defense as a linebacker. I'm 6'0 and only 145 lbs, but our team is really too small to have like second or third strings, pretty much everyone starts somewhere. This is my first game and I don't know what to expect. Honestly, our defense barely got worked due to the hurricanes we've been having lately, we haven't had very many practices. We also had to go light on hitting because we only have about 20 players and if we lose anyone then we're done. So anyways, tomorrow is our first game and quite frankly I'm pretty nervous about it. I don't want to screw up and miss tackles or something or fail to do my job and have the team hate me because I made us lose our game. It is a preseason game, but still. What do I need to do and what kind of mentality do I need going in there and coming out win or lose, even if the loss was due to me?