
I am sorry to say I think you will have to put it down to experience, I don't think you will be able to do anything about that now, you accepted the in store price yesterday and went ahead and booked at that price and if you try and cancel the holiday you will still be liable for the full deposit not just a low deposit if that is what you have already paid.
I know it is of no use to you now however remember for future holidays it is worth checking the price online prior to visiting a travel store and trying to get them to match the online cost.
The one thing you could try, which to be honest they probably won't do, is ask if they could include some type of extra such as pre booked seats or include in-flight meals if not already included, ask you never know.
Graham