Dodgy looks and achey joints

First day of training and I can honestly say that running is most definitely NOT my hidden forte. It hurts. I got funny looks and dodgy comments thrown my way whilst running through the park, and to say I'm unfit is a UNDERSTATEMENT! I managed around 1/2 mile around Hanley Park (ok I'm probably lying it was more like 300 metres) before I felt like I had been drop kicked in the chest by an angry athlete. I'm still going to play the asthma card a little while longer, to conceal my lack of fitness. You never know it might win me the sympathy vote when I finish the 10K in 7 hours 49 minutes, crawling across the finish line or worse carried across in a stretcher.
No. I need to remain positive, I will complete the race!
Is it too late to back out?