I hope the island (and hotel) doesn't turn out to be a disappointment for you.

If you are so inclined, it's worth some hiking to one or more of the viewpoints (I like Mango Bay viewpoint). Make sure to hang out on Sairee beach for a sunset and if you're into Chinese food you have to drop by 995 Duck for a $1.50 bowl of duck noodles which is one of my favourite meals on earth. The island is obviously most famous for its diving, or a longtail to Ko Nang Yuan can be a good way to kick a couple of hours.

Edit: If you do want to stay at Blue Tao (e.g. for the last night), you might want to email them from their own website. They don't always put all their rooms on booking.com for reasons that nobody has ever been able to explain.