I'm 12 5'2 120 lb girl I have a fancy choir concert in 4 days I can't wear jeans I have to dress fancy I am really fat all over arms nd legs nd stomach- what can I wear that's flattering?

You only weigh 120 lbs and are 5'2''. There is no way that you are "fat all over." I'm sure you're adorable. Wear something you're comfortable in that is made with a thicker fabric so that any imperfections are smoothed over. But mainly, take a look in the mirror and realize you're not fat at all. Embrace your natural figure and be confident. That's the most flattering thing you can do for yourself.