Luana
Just a nit picky point but better to correct it now than later. When you send the dog for the sheep ,turn to face the sheep not the dog, this cues him to where the sheep are located. Also don't handle (touch) him to set him up, instead move forward a bit and call him to the side you are sending him. When sending use a verbal command (or as some do so as not to give a wrong command , give him a sshhh sound ) and do NOT give any physical gestures such as flicking you stick, moving toward him as he is leaving etc. This puts pressure on him at a time that you don't want pressure.
As others have said above ,get to a bigger field. Don't practise too long ,many short sessions are better.
Good Luck