Every online source seems to agree with the preconceived notion I had that the correct usage is "worshipping" with two p's, saying that "worshipping" is an exception to a rule about doubling the leading consonant when the preceding vowel is stressed. However, the spell-checker in my browser seems to think that the correct spelling is "worshiping".
This leads me to believe this must be one of those interchangeable British/American things (e.g. "colour/color"). I can't find anything about this on Google, as it just returns a bunch of articles about religion, failing to understand use-mention distinction.