If you keep the speed as constant as possible, the plane will be less likely to veer off track.

Plenty of power as you pull up into the loop and then gradually ease off the power as the plane goes over the top and back to idle as you go past 3 o clock. Then gradually increase the power again and have plenty of power on again as you start to pull up into the second loop and so on. You will also need to constantly adjust elevator to maintain the correct geometry.

The best way to correct for coming in or going out on loops or part loop maneuvers, is to use the ailerons. If the plane is coming in, then lower the outside wing slightly and if it is going out, lower the inside wing. This will be less noticeable to the judges and eliminates the chance of wrong rudder input.

If the inside wing is down and you use opposite rudder to correct, the plane will get all crossed up and look terrible. So concentrate on keeping your wings level and use rudder to wind correct in level flight and verticals.