Descriptive Writing Help? (URGENT)

I'm really struggling with questions that focus on your descriptive skills, I'm doing the IGCSE Edexcel exam board and for the creative writing section I've been getting really high marks for questions that ask about explaining and informing (around 17/18 out of 20) but I always do badly when it comes to describing (I get around 8-12 out of 20) My teacher said it's because I write like I'm writing a story, but I still don't get what I'm doing wrong? Could someone please help me with some tips on how to get a higher mark as I have my exam in two days or provide me with some links that help with descriptive writing (my teacher said that my writing skills don't need any improvement, it's just that I'm not 'answering the question properly' when I get a describe question.)