Sorry Rosie but i dont know what machine you have got but i am assuming it is either a maximist or a t200.
If you spray up and down you need to have the dial at the front of the gun set to 6oclock, this will give you a fan pattern which will enable you to cover the body quickly whist minimising the amount of solution you use. You need to be approx hand (6 inches) distance away from your client, that way you will not fill the room with overspray. Secondly, you only need to open the density dial at the back of the gun approx 2 half turns to the left.
Practice spraying on couch roll so you get a feel as to what is going to come out of the gun.
alternatively, if you spray left to right you need to adust the spray pattern to the 9.15 pattern (ie left to right) This rotates the fan shaped pattern
if you set the dial on a diagonal, your machine will produce a jet, all this does is make your spraying time longer and maximise the amount of solution you use which will make your clients appear wet. Sienna don't recommend this way of spraying at all.
I would suggest maybe getting back in touch with your trainer