Hello,
The allotment of seats under category b is totally based on the candidates applying for seats under category b. If there are not many people with a better rank than yours', then you can definitely get a seat. In the other case you may not get a seat. We can't just say if you can secure a seat.If I say you are/aren't going to get a seat there, there are great chances for me to be wrong.  I hope you can understand. 
Hope for the best!