addressing a deficiency in an intent letter

I am waitlisted at four schools but have one in particular that I am extremely interested in. My overall GPA is at the average and my MCAT is above theirs, however, anyone who looks at my application will easily notice that my science GPA (3.14) is my main deficiency. I never addressed it in my PS but I am thinking of writing a new letter of intent today and wanted to know if it was appropriate to address and explain it without making excuses? Has anyone done this and got in?