Help: big trouble, thanks!

I didn't change J-1 to F-1 after I got J-1 waiver since a J-1 friend told me that J-1 can stay 18 months after gaduation. I also went to international office in my university, they said there is no difference.

I will graduate in April, 2004. I recently knew that J-1 holder has to get a job offer before graduation to apply academic training. I am not sure if I can find a job in the several months left.

Is it too late to apply a change of F-1? It will take how long usually? What can I do if my present advisor refuses to write a recommendation letter for me to apply my academic training.

I have to go back to China before June, 2004 if I fail. Any suggestion? Thanks in advance.