Total Wardrobe Freakout!

So parents are having a big Ruby Wedding Party next week. They're basically having the wedding reception they didn't have back in 1970 as they already had four children under ten between them when they met and the whole wedding industry was in its infancy back then. Dad was a widower and Mammy an "unwed mother" (gasp!) and they found each other and lived happily ever after or at least as much as you can in the real world. All five of their children (they had one together 18 months after the wedding) will be there including the brother who is flying in from Andulusia and the sister who is flying in from California. I'm hugely excited not least by the fact that they're having the same caterers we had for my wedding and I'll get to really enjoy the canapes without having to pose for photos the whole time.

However...
I don't know what to wear. I have body image issues at the best of times (English size 18-22) and find formal wear stressful but when in the company of my sisters the situation reaches crisis point. My sisters are slim. And beautiful. My youngest sister was briefly a model. She's six-foot, a size 8 and has that enviable ability to look effortlessly elegant, poised and gorgeous. Next to her I look, dumpy and scruffy and slightly chaotic.

I went into Monsoon yesterday and tried on some dresses. Oh my good lord...sack of potatoes anyone?

Then my lovely friend BermudaGirl lent me her party dress

It's beautiful and I got myself a shrug in the Monsoon sale so I won't have to show my hated upper-arms (and the tattoo my dad still doesn't know about,and a BARGAIN pair of bronze shoes from ebay (£3.98 including postage) and then I tried it on. I can't get the flippin' zip to do up. I'm hope, hope, hoping it's just I'm at the wrong angle and someone else will be able to do it for me and will be taking it to MrsB's with me later.

But, just in case, I've also ordered a dress from ebay...

It's plain but will look great with some retro accessories(polka-dot shoes, a red-velvet rose in my hair, scarlet lipstick) and I love the full skirt.

What do you think?