About 35 laps I think (about 1km a lap).
Don't worry, you'll be fine. If I can race there you certainly can.
If you finish in the bunch you'll have done excellently on your first time as it is tough racing. That said last week seemed a little bit slower than before (Stu, George, Sylv etc all now 2nd cats so that may be the cause as the real flyers have moved up a cat). Agreeables will work together if possible, but just find any safe looking wheel to follow. Most riders at Palace are pretty good and safe.
When I'm dropped I've just carried on as best I can to gain more experience and get a good workout. If possible try and hook up with others to form a partnership you can work in.
If you can get there early then it will help. Race start is at 7:15 with the youth races before. If you can get there from 6pm then you get a chance to do some warm up laps and familiarise yourself with the circuit before the youth race.
Good luck and see you on Tuesday.