In reply to:

I'm going to be staying at the Marriott Marquis on Broadway soon. I mentioned it to my friend from DC who was staying. "You can't stay there," she said, "until you learn to pronounce it properly!"

Any idea as to what I'm doing wrong?

it's hard to tell when you chunter like that.
does she want you to say 'mar key'? [as opposed to ma[r] kwis]