Thank you all for your comments and advice, unfortunately things didn't go according to plan for me.
The Saturday before the event I was at the club shooting very well at the plinking, missing only just a few with first shot. I was very happy with my setup it was going perfect. With high hopes for a good score the following day with winds predicted to be the same I finished the days shooting on a high. I refilled my AA S400f and went home for an afternoons cleaning ready for the next day.
I got home place my gun in my homemade rifle stand cleaned it and left it there ready to put away after first some welcoming dinner, picked up my dinner the wife had made walked into the dining room when i heard this very loud hissing noise...! It was a seal that had blown on the end of the filler and tank. I hadn't over filled it, I can only put it down to heat differences from being filled outside being brought into rest in a very warm kitchen. Luckily I had ordered a complete set of seals ready for days like this at hand.
Anyway I replaced the old seal with a new one but as I did I accidentally turned the barrel slightly which meant it was now not zeroed.
Next day the day of the event I quickly filled up with air and tried it plinking and just as I thought it was way way out of zero.! I tried my best in the time I had to zero in but to be honest I was very happy with the setup I had the day previous.
I got to say a big thank you to one bloke that was there at the club I have only every seen once before briefly who offered me use of his spare PCP if mine failed to work out and his name is Phil.. As "Strokebloke" mention a great guy that will look after you "Phil Hollis"
Anyway I didn't take Phil up on his offer as I wanted to go round with mine which I did. I didn't score as good as I'd hoped only scoring a miserable 10 but I had a great day and look forward to the next.
Thanks again to all for help and advice.