Please excuse me jumping on your post but I'd like to explain what happens for those in your position.
You can only shoot and score points for the region in which your card is held.
Each region pays £75 to enter the event.
If a region does not have a full team then they may sell their cards (£5 each) to people who are not in teams but would like to shoot
(that's usually the only way I get to shoot
Unfortunately this offer cannot be extended to everyone because there's potential for the event to go on and on so there are only 9x15 cards available. However, I've never known a shooter who attended on the Sunday and wanted to shoot not being able to, albeit they usually have to wait until the end of the day (with 135 shooters it will be a long day).
One final point - this is my first Champs/Inters away from Newbury so I am offering information based on my experience at Newbury.