Welcome to the forum Neil. I had an Airflo line once and had simalar problems. It's called memory i.e. it rems being coiled up on the reel. You could try, before you set off, stretching it. Go into the garden and put a nail in a tree, hook the end of the line to it and get about 10-15 metres off then pull like hell and attatch it to something so it remains taught. Leave it for as long as poss, 2 hours maybe. Reel it back on, not to tight, and it should be ok when you get to the water. Before you start give the first metre or so a good stretching by hand.
Alternatively go to trade classifieds on here and look for Barrio fly lines-buy one of those for 19 squid-problem solved. HTH.