KKat - I couldn't swim a length of FC this time last year. In fact I couldn't swim a length until about February of this year. In Austria I started a minute after everyone else and let them get on with it. I bumped into one person and the canoes on either side of the course but made it home and I am the slowest swimming pirate on the planet!
I hate swimming but I went with the plan to finish just within the cut off of 2:20 and ended up finishing in 1:47. Still slow but I was so chuffed cos I knew that the worst bit (for me) was over.
Get a swim coach, sort out technique (I've never managed to do that) and the distance will come.