unity 3d urgent

we are using unity 5.2.2f1 our game is about animals who revolted and are attacking. you (the player) stands in the middle in the forest (or world) and can rotate around to see the animals that are coming at him (you the player). he needs to shoot them or else he would be hurt and eventually game over we already have a world set up and we have animals being spawned from the trees. we are trying to get the player in the middle (so a first person shooter) and shoot the animals. can switch with guns 1, 2, and 3 keys as each gun does certain damage. the assets have to be free from online, unless they are bought. so basically the player stays still in the middle of the world/forest, and is supposed to rotate either with keys A & D for left and right (to view all the envirnoment around him) or if its hard it can be done with the mouse as it is already if you import a first person prefab in unity. i tried doing that but the mouse gets off the boundary of the screen ....like the player has to drag the mouse all the way in order to rotate but thats not practical. the mouse is also documented to aim and shoot at the animals.