birdies, pet, I'm sorry you're in such a muddle. As I've said, I'm sure everything will be ok; maybe baby just took an early spurt, and is now where it should be. With DS my date changed every time I went for a scan, as he never measured spot on according to one specific date - also different sonographers make a difference.
Look at it this way - all the measurements taken now are relatively in proportion 11th, 19th and 37th percentile sound like a nicely formed baby. If you had one tiny measurement, and the rest were all bigger, then there would be more of a worry. The measurements are never all on the same scale anyway, i.e. not all 50th. I think mine this time at 20 weeks were something like the 50th (tummy), 60th (head), and maybe the 75th (femur)? Something like that anyway.
As for babybond, they really are excellent. They are all hospital sonographers, who are specialised in doing these scans. If you want to be seen sooner, I would absolutely make an appt with them. They're very thorough, and if there is a problem, I would absolutely trust them to pick up on it.