Wait, did you equip the ritual gemstone? The steps are as follow: you find the magical gemstone in the first temple, find the secret room in the second temple to turn it into a ritual gemstone and then you equip the new stone when you want to use the spell.
Viewing post in Caliross, The Shapeshifter's Legacy comments
Equipment doesn't appear in your regular inventory, but it should appear in the "charms" sub-section. Anyway, if you did everything right you should be able to equip it in the "accessory" section of your equipment page. If you checked already, maybe send me a link to your savefile, and I can try to figure out what went wrong.