How to fix not being photogenic

We got the rest of our engagement pics back (I'll post them later), and I really do love them... at least I love about 1/8th of them. I just wasn't born with that photogenic gene. My sister can take an "ugly" pic and look fab, while I thought I was doing alright and in so many of them I have super double chin, a weird lip thing, no chin at all... I don't know what happens! And I think I'm relatively pretty in person, not a model but I have a lil' somethin'. It's so frustating! My FMIL says it's just my personality, that I'm a little goofy and very genuine so that shows (which is good... until I want beautiful pictures). Like, when I smile, my eyes practically disappear no matter how much I think about it. Or then my smile looks fake. Or if I think to hard about my face, my posture collapses and I look like I have a hump. Ugh. Does anyone else have this problem or know the best way to at least look nice for wedding pics? One day, that's all I want...