I have already applied for change from b1/b2 to f1 (now pending). I20 is for fall 2010. School has just started and F1 is still pending. What should I do now. Will this have an effect on the decision of immigration. Can I change it to Spring instead?

Get a new copy of I-20 and return to your home country ASAP before you overstay. Apply for F-1 from your country.