I have an order for a cake that I under quoted.   The reason that it happened was because I am making a flavor I have never made before and the ingredients cost significantly more than what I normally use.  Would be it wrong to ask for more?  I'm making absolutely no profit now because of the the cost of ingredients  .

It's more wrong for you to make no money!  Apologize and explain.

Ok I checked back in our conversation and realized I quoted her before she told me that she wanted a "premium" flavor. And I had no idea that the filling would be so expensive.

Hmmm...Usually if you make a mistake like that you should eat the cost and chalk it up to a learning experience. But if you haven't made anything yet, I'd call her and tell her that the flavor she ordered is more expensive than what you quoted, and that you can do something similar for the price you quoted, then give her some options.

If you're REALLY not making any money on the cake because of a small error like that, though (and that should be a small error) you need to reevaluate your pricing. The cost of ingredients shouldn't be so high that a mistake like that costs you all of your profits.

So now you can honestly say a premium flavored cake will cost $xxx - no guilt, no fuss, just the facts.

I think you are within your rights to ask for more because the contract isn't signed but I personally not.  If I made a mistake with the quote, that's my bad.  I would be a grumpy bride if the price upped a lot after being given a quote unless I had either changed something.  Sorry to be cold, but as a bride, I would have expected you to check the costs before sending me the quote.  Is there a big difference?

Also, like Costumeczar said...if this one error in filling price has wiped out any profit then you  are not charging enough.