Well done on stopping smoking and losing weight! Just get out there tomorrow and enjoy yourself. I also doubt you will be last with your time but the most important thing is to have fun. So go and do it. You have done all this training so please don't doubt yourself. You will feel great crossing that finish line. Good luck and let us know how you got on.
Good to hear that you are still enjoying your running and that you are listening to your body and moved the goal from 8 to 10-ish weeks. It's still a short time to built up to 20 miles so please continue to listen to your body and don't push too hard.