Hey, tournament player here. Watched your video. I notice two flaws in your gameplay: one is that you roll way too much, and a good competitive player will abuse this. Every time you were facing any kind of pressure vs. that ZSS, you rolled away. I know that it can be a difficult to not roll, but really the best way to get around is by walking, and you should try to force yourself into the habit of walking everywhere instead of rolling. Rolls and dashes are options that you use when you know that your opponent won't punish them.
The reason for this is that rolls and dashes move you a set distance and don't take you exactly where you want to go, and the actions that you can take during a roll or dash are limited--you can't act until the roll or dash animation is finished, once it's been initiated. Walking is much more in your control, as you can stop at any time and perform any action. You aren't committing to a particular animation. In competitive play, the player who commits to an action first (aerial, attack, roll, etc.) is the player who will lose. Don't commit. Leave your options open.
The other thing that I saw you doing is hiding in your shield. Don't ever just hold shield and sit there. This is the surest way to get read and grabbed or subject yourself to shield pressure. You should get in the habit of briefly flashing your shield right when you think you're in danger of getting hit, and letting go as soon as the danger has passed. Hold the shield only when you've actually been hit (this will require good reaction time but it gets easier with practice).
If you try to correct these flaws you will be a much better player: you have a good sense of timing and when to attack/not attack already.