I think that happened to me as well. I was checking prices for inside, oceanview, and balcony cabins. When I finally chose a cabin and booked, my total was more. The additional amount tied to the port taxes and fees that showed up on the final invoice.
As a further rookie mistake, I thought I was putting down a deposit with final payment at the 120 day point. Imagine my surprise when the entire amount came up on my cc statement. I must have missed a box that was already checked “pay in full.” I will not make that mistake again. I was able to walk it back to only deposit easily enough.