You dash attack way too much on the approach. If you're going to do that, at least space it so you end up behind him, so it's a tiny bit harder to punish.
You look for the fair way too soon, and in places where it won't set up an edge guard or get a kill. You can platform dash to grab onto platforms and such, no need to try for the finish so fast.
Use your needles more carefully. Like when they'll actually hit him, or when he's not close enough to dodge and hit you.
Wavedash out of shield to grab to punish fsmash. Kid stuff.
At 2:40ish, you should've gone in with a grab to punish his lag, then followed up with a uair or a fair. The dash attack is not going to kill him, and at that percentage, it's not going to set up for anything either.
Light shield edge hog. It's way more consistent as an edge guard. If he tries to go high or pull something fancy, short hop out of shield into a bair. Your crouch cancel stuff won't always work.
Sheik's dash dance is bad, but not non-existent. Use it. Don't wavedash everywhere.
Errr... learning to DI out of combos and... surviving those tippers would be good.
It feels like you're spending too much time in the air. Being above Marth is bad news.