Its all about confidence mate. If you havent already, I would recomend buying a new pealess whistle (I and many others use the trustworthy Fox 40 classic) and make sure you are loud and confident when blowing it. When you signal for throw ins, try and make sure your arm is a little bit above the 90 degree angle. Like make sure your arm is either straight, or pointing up a bit as I feel this makes you look a lot more certain of whos throw it is, than if you arm was slouched and pointing down. When reffing younger age groups like U10, be vocal and make sure you sound confident and have confident body language. For example, if its a corner shout something like 'corner ball' as well as signalling as young players dont normally understand the signals. Try not to slouch or look like your having a hard time if its a tough game, as players will pick up on this and take advantage. If you give a free kick for example and a player says 'thats not a fould ref!' have a word with him and make sure he knows your in control. In my first 6 or so games, I struggled massivley with match control but confidence will come over time, and you will learn that your decision is NOT wrong, just because the goal keeper who is 60 yards away from the incident claims he saw the player 'win the ball'
and whatever you do, dont favour your decision to one team because they keep having a go at you and you just want it to stop. Have a word with the manager and let him know your decision is final. If you do give in and let a spectator or olayer influence your decision, you will lose the respect of both sides, and thats not good!
All in all, just enjoy yourself out there mate! In 3 months time I guarantee you will be shocked at how far you have come. I find refereeing so enjoyable because I have gone through that stage of worrying about making a mistake. Players dont score every shot, so dont worry if you have a bad game! Every ref has them, just make sure it doesnt go to your head