Hi there
Everything is logged on the servers at every step of the purchase process so you are not in danger of losing your platinum.
However sometimes delays can happen between your device and the Apple server confirming the purchase, these are most often internet related delays with the message somehow not getting through from your device to the Apple server.
There are a few things you can try:
First stop is to have a look at this support page and follow the steps outlined:
http://celtic-heroes.com/support/suppor ... um-issues/
Make sure you are playing on the same device and log into the same account as you purchased the platinum on.
Try a different connection (e.g. if you are currently on wifi try 3G, or try a wifi connection in another place.
Try turning your device fully powered off and back on.
As mentioned above there's no danger of actually losing the platinum but it helps to try and nudge things along if there have been delays verifying the purchase with the above steps.