Awww damn...you gave the check back?!
O.K. 1st off you hit it on the nail yourself with the confidence thing. You definitely have to resolve this within yourself and quick if you're doing this calilber of orders. But let's say that you WERE confident and still didn't like the cake (after all, we are our own worst critics as it has been said before)...the bride said she did, so end of story.
So what should you have done?...let that crazy aunt know "I'm sorry, I don't know where you are getting your information, but the bride herself gave me approval AND payment for the cake and I am in no way authorized to speak to you with whom I have no contract with. But you can let the bride know that if in fact there really is a problem, she will need to call me direct...she has all my info. Enjoy the rest of the reception". (ole heffa)