The course on Sunday will be very hard work if it stays wet. You might want to swap your trainers for football boots if you have some.
What size feet do you have?
If you get lapped on the grass playing field, as they go past you speed up and try to stay with them for as long as you can, particularly if it is into the wind.
Otherwise, remember the numbers of the two or three riders immediately above you in the last few riders, and don't let them go. They are the ones you need to aim to beat. Make sure the ones that you have beaten don't get past and away.
Who is coaching you at Redditch R&P?