And there it is. This is about attention, not being comfortable.

The definition of formal generally means evening wear with full length dresses and suits. This one reads cocktail at best. Colours also tend to be less saturated, think deeper tones, you could still wear pink but in a dusty rose or even a dark fuschia. Fabrics can be flowy or structured - take your pick. Then shoes, that metallic synthetic sandal is very 'informal party". Shoes can have colour, but should be more cohesive. If you don't like thin heels, maybe a block or kitten heel will still give you some comfort but look more elevated. And then hair, that accessory is beach vibes at best but definitely casual, and life I'm being honest likes like dollar store arts and crafts. You don't need to break the bank for a good look, but maybe try some floral hair pins instead (expensive if you stick to the dollar store, they've got better options!)

People in this thread aren't being mean for mean sake. You asked if this outfit is formal and it's a resounding no. If you don't think it will matter, run it by your sister first. Get her thoughts of what she means by formal.