That looks like it might be a little too tight. Can you get vet wrap there? That would be easier to use since you can get that in much wider strips than the material you're using. Vet wrap is also stretchy, so it's not as constricting. Since ducks use their wings for balance, it's normal for them to be unsteady when they're wrapped. You can use the pics in the first post in this thread as a guide-->
https://www.backyardchickens.com/t/736147/how-to-fix-angel-wing.
You can't feed them just fruits and veggies because those won't contain all the nutrients he needs. He should have a good quality duck feed or all flock feed in addition to his veggies. If you don't have duck feed available, you can sprinkle some Brewer's Yeast on his all flock food.
Really glad you caught this in time!!!