I watched your set against tutu zinoto. Use more side-b, it's really good vs sheik I find. When you're playing you seem to play like the same when you're at low %s or high %s. When you're at high percents you need to camp more because when you get to a certain point in damage it doesn't really matter if you're like at 180% or 220%...pretty much anything will kill you so taking a bit of extra damage is fine as long as it's not a kill move and since your camping and your opponent is trying to hit you with a kill move then you kind of know what moves they'll choose and to be ready for them while you're camping which leads to massive punishment. Tutu used a lot of dacus for kills when you were at high percents so camping back with a banana or two would have really weakened that strategy. You need to mixup your landings more with B reverse popguns you got a good amount of damage. I don't ftilt lock really matters that much in this MU, you'll get hit by a couple, but the only way for them to continue it for a while is if certain conditions are met that are situational like how stale it is and what % you're at. If you get into the ftilt lock just mash up on the c stick and direction pad since you can uair and it comes out frame 3 which is super fast. Sometimes it's best to just midair jump out though if you're high enough. Sheik can get most of the damage by edgeguarding you and juggling you, tutu didn't really rack up a lot of damage by edgeguarding you though, but if you're playing a sheik that does just recover low, it works better usually. You should be more patient with your banana throws, game 1 you weren't really that patient, but games 2 and 3 you were a bit more patient, but it would've been better if you were more patient. That's where side-b can also come in and help you as a mixup. You also need to be more patient when you force your opponent into a situation. I see you dash back a lot which is REALLY good in general it helps with stage control so much especially when you have a banana in your hand, but you also dash back when you trip an opponent and then dash back towards them to punish. That's fine and a legitimate option, but it looks like you kind of use that as a marker...like you could just stand still and have the same result which is what you should do more...just stand still and wait for your opponent to do something, but it seems like you always want to be doing something even if it's just a simple dash back. Again, like if you trip an opponent dashing backwards and then dash forward back at them is fine, it's just a substitution for when you could just be standing still. I saw a couple of times where you forced tutu into some situations and you just immediately spotdodged or rolled or threw a banana when you should have just been patient and waited for tutu to do something and then punish.
The main points: Side-b more, b reverse popguns more, be more patient.