I feel like I've been tricked by my fiance.
Why do you feel like you've been tricked by your fiance?
She wore such a lousy dress when I proposed to her.
Having a special moment like proposing your fiance being the best setting possible is the most ideal situation. If the situation isn't perfect you shouldn't feel like you were tricked or anything along those lines, you should stick with your plan even if the situation doesn't meet all your expectations. If you continue to harbor these feelings of being wrong because the situation wasn't perfect for you, it can result in problems in your relationship.
I think I get what you are saying.
Proposals are generally a surprise. Like she didn't know what was going to be happening. You could have asked her to wear something nicer or bought her a dress for the special occasion.