suzie 2;i can assure you that joining a running club will get your times even lower.i myself am not a member(just enjoy running,not up for racing)but people i used to leave behind have joined a club over the last couple of years and now they leave me behind.
as for feeling bad,i think it would help if you got your body used to running the distance,pace,etc.you may also find that recovery will improve as well.
i was looking at folkestone or maidenhead on the same day.but decided to concentrate on training runs until end of the month.
have a 5 mile and then a 10 mile,10k in may before southend 1/2.
good luck at folkestone,what sort of time are you aiming for?
going by pw time,i would say around 74 mins.no pressure!