How can i get a student visa the second time?

i have completed my engineering in computers and now i have got admission in the university of bridgeport for the summer session 2011 . i completed my engg in 6 years and have a total of 24 backlogs but now i am done with my degree . when i went for the first visa interview , i was rejected and she said that i am not a legitimate student . i cant change my graduation marks but i really wish to to do well in future and go to usa for my masters . i really want to pursue this course from the united states itself . can someone help me through this and tell me what changes i can make for my next visa interview or is it pre decided my the usa embassy . can their decision change . i am ready to do what it takes but just tell me what