Yeah your GP has gone about telling you most things the wrong way but you should and by the sounds of it already have used it to motivate you to join Slimming World. You will probably be thanking her for being so brutally honest when you reach your target.
I wish someone had been like that with me years ago instead of being so nice all the time.
I lost 15st in 10 and a half months last year and i lost 13st 10lbs of that on slimming world. Just follow the plan 100% and try adding some exercise in and you will be shocked at the results that are possible. You wont need a Gastric Band fitting either, you just need to get your mind in the right place and everthing will fall into place.
I weighed 30st Jan 1st 2012 and am now around the 14st 10lbs mark and have been since Nov 20th 2012. It really has completely changed my life around. I am now the manager at work and had 3 pay rises in the 10 months i have been in charge! which is crazy haha. I have also recently found the women of my dreams who is so stunningly beautiful inside and out, kind, amazing, so loving to. She has completely changed my outlook on life, she is INCREDIBLE and accepts me for who i am.
YOU can and will do this just believe in your self and the rest will follow. I hope you enjoy your fist class today