Firstly, don't take the GMAT unless you really need it.. So if your school needs a 550 and you are not willing to compromise on the school, then go take the GMAT again..
Secondly, take time out of your hectic lifestyle and study for the GMAT. Plan your study and stick to it. Studying for 5 months or a year doesn't mean you score higher.. There is an optimum level of study that you need to do to get your best score and that level differs for everyone. Ideally 2-3 months is perfect. Anything more is a waste of time and usually does more harm than good. Anything less is a waste of time too because you don't score much at all.
My suggestion would be to compromise on the school and apply with a 510. If you get rejected, you will anyway have to take the test again.