Unless you're going to be camping miles from a supplier (there's usually a little symbol for gas availability on site list entries, though it may not indicate which type) I wouldn't worry too much - you may well have only used about a third of it!
Take Rockford's advice and give it a shake - if you don't feel any liquid sloshing around it's probably empty.
We did the sloshing and weighing trick last Aug bank holiday, knew there wasn't much left in it so asked the campsite if they would keep a 907 by for us (they know us) and said I would swap it on the sat am if it hadn't emptied by then - that way dofo would have gas for sun & mon.
It ran out just after cooking breakfast on Sat am!! Perfect guessing.
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets