I'd wear it.
Where does this ridiculous thing about not wearing white to a wedding come from? Aside from the fact that many brides don't wear white, who is going to mistake you for the bride? Literally everyone there will have been invited because they are a close friend or relative of the bride and groom, so they should jolly well know you're not the bride! Plus the bride is the one walking up the aisle, standing at the front saying the vows, posing with the groom for photos, riding in the fancy car, having more photos, sitting on top table, cutting the cake, doing the first dance. You'll not be doing any of these things. You'll be at the side holding a clutch bag, an order of service and a box of confetti.
And even if someone did by some bizarre turn of events mistake you for the bride, what would happen next? You'll just say, "Actually, the bride is the one holding a bouquet over there, with everyone fawning over her" and the day would carry on. You won't end up accidentally married to the groom will you?
People are weird.
But if you're in doubt, ask the bride or choose something else.