Tiled Shower Surround Help
I have, what I perceive to be, a big mess. Here is my situation. I've recently torn out an old one piece fiberglass tub and surround. I've installed a new tub and I am prepping to install a porcelain tiled surround. I've installed all of the Hardiebacker without any major problems, but then I made a stupid mistake while prepping the transitional seams from Hardie to drywall. You see, I am not taking the surround all the way to the ceiling, so the Hardiebacker will be meeting up with drywall along all the top edges and two side edges. All of the drywall is pre-existing drywall that has been painted except one spot above the surround where I had to install a piece a green board. I haven't taped or applied thinset to any of the interior Hardiebacker seams, but I was stupid and applied tape and joint compound to the seems between the drywall and Hardiebacker. I read that I should not have used joint compound on these seams, so I attempted to remove the joint compound so I could redo the seams using thinset. My attempt at removing the joint compound is failing miserably and I'm afraid I'm screwing everything up. There are spots along the edge of the green board (where it meets the Hardiebacker) where the the green paper was peeled off when some of the joint compound was removed. It is probably important to know that I plan on having the tile overlap each of the Hardie/drywall seems by less than an inch. Here are my questions:
1) What is the most logical way to remove the joint compound? Some areas have as much as 1/8" thick to make a smooth transition from the Hardiebacker to the drywall.
2) What can I do to remove the joint compound from the green board w/o further damaging it?
3) What can I do about the spots of the green board where the green paper facing has been peeled away? This is a major concern as it is along the seam above the surround where the Hardiebacker and greenboard meet. Will priming and painting the greenboard before applying thinset help make those "bare" spots a bit more moisture resistant?
Sorry for the long post, but any and all help will be greatly appreciated. Thank you!