when relying on your dad, do as he says. but only for those rides.
going to your sister's wedding, wear something as male as you can, until you get there. then ten minutes before the ceremony starts, change into what you really want to wear. i'm sure you're allowed to bring a bag with an extra change of clothes, hide something nice in there. even if your dad pays for the wedding, i doubt he'd start a commotion with all the guests present. and if he does, tell him you're a girl, it would be improper to wear pants. and be loud about it.
in order to get rid of that guilty feeling, you'll have to realize deep down that there's nothing to feel guilty about. and that your father does not dictate the morals and ethics of this world, much less your life. for me, that comes down to making a decision and sticking with it. i did feel self-conscious about wearing male wear in front of my parents (not out yet, but still). then suddenly, my uncle says that that was the most he's ever seen me look like myself. i've never felt anything other than comfortable in the clothes i like to wear, after that. looking like myself must be the greatest and most proper way i could ever possibly look. if my parents disagree, that only means that they don't see me for who i am, and are trying to make me into something i am not. they are the ones making a mistakes, they are the ones who should realize their guilt, they are the ones who should feel sorry. and if anyone has to apologize, it will not be me. for i am only doing what's proper and good for a person like me.
try getting that into your head, so well that you can feel morally just about wearing gender appropriate clothing. don't pretend to be a guy, unless it's a demand in order to get something that you want bad enough to do that. you are a girl, act like it in every situation where it isn't potentially life threatening. if you keep at it, you're likely to see that most people are ok with it, some might even give you positive responses when you go out there as yourself.
also keep in mind that there is no point feeling guilty about making the right choices for your own life. just the same as how it usually feels horrible to make the wrong choice, if you know it's wrong when you make that choice.
do you think a cat feels guilty about it's fur color?