Oh where do we start.
try riding a mountainbike more ;-)
Guessing the problem is the lack of spped work, you need to do some interval work and some bike handling skills work.
Most people go out for a ride then try and race, you have to ride like you race more often.
go out find some tricky corners and do them hrad and fasty over and over and find the limits, and blow your brains out trying too.
then that start line frezy will not be as much of a shock.
OR....just join plumz and you will become naturally gifted, just look at Glynn this year
;-)