How to complete 21km?

The date to SCB Marathon 2009 is drawing near and I am not ready for my run. We have been training regularly but we are quite behind schedule. We are about 5 weeks away from the race and I am covering only 12km which almost kill me, how to complete the next 9km?

I am quite a blister queen, I have developed blisters at different part of my body weekly while I run. I had a blister on my shoulder cause by my sport bra and I have different blisters forming on my feet. The very wise conclusion from my colleagues and friends is, my shoes is Either too Tight or too Loose..(As good as no Conclusion!!!)