I can't use a gem premium plant I bought on iOS

After roughly a month of playing the game, I had enough gems (legitimate, not bought) to buy one of the premium plants. I chose to buy the Dandelion (as it was limited time), and confirmed the purchase. My gems were spent, the Dandelion was in the almanac, but when I went to try it out in a level, it showed it as if I hadn't purchased it. When I pressed the buy button, it gave me the option to buy more gems. I don't know why this happened, and how to get it back, but don't think I will put the game down just because of this. I'm really enjoying it. By the way, I'm using an iPad Mini. Help would be appreciated, thank you.