Mushrooms are very tough to glue directly. Get a little tupperware and put a layer of either crushed coral or rubble rock in it, along with the shroom. Cover it with a piece of netting and put it in a bright, low flow spot. In a few days it will attach to a piece of something that you can glue.
all good advise above ^ I have had good success doing it like this vid, I have tried gluing them with little success - just go to a fabric store & pick up a foot of bridal veil
Take some fine mesh like net mesh or pantyhose and select the rock u want it on, use a 3" Piece of pantyhose or loose net, trap the shroom against that rock. in a bout 3 weeks, It will settle in and attach
You can also "sew" it onto a place you want it - just thread the needle through the tissue as close the the base as possible and then tie it down. The foot will attach and then you can cut off the thread.