Is it difficult to get into chelsea college of art and design?

I have applied for MA in Interior and Spatial Design at Chelsea college of art and Design. I have a good portfolio but my college percentage is 56 %. Most of the colleges I applied to in UK asked me for a 2:1 honours degree, which means 60% or more. I got an offer from University of Southampton, Portsmouth, University of creative arts, De montfort. Middlesex university also requires 2:1 honours degree. I am just 4% less than what they are asking for and I have a good portfolio. Are these conditional offers negotiable? And I am still waiting for reply from Chelsea. Its been more than 20 days since I applied. Is it difficult to get into chelsea? Is there a reason why they are taking so much time to take a decision? Please if someone has an answer.