What if people wonder why I move my shoulder blades and blink a lot?

Some people may wonder about certain habits you have, but the amount of time they spend thinking about them is much less than you might think. It's so hard to comprehend that. In reality people may notice a habit, but they quickly move on to seeing or thinking other things. If you are concerned about these habits perhaps you might want to see someone to determine the cause.

Let them wonder. If people are judging you, it means that you're putting yourself out there in the world despite your discomfort. That's huge. Keep putting yourself out there. Your tics are part of a medical condition you can't control, and anyone judging you negatively for them simply doesn't understand what it's like to be in a body that doesn't quite want to behave in spite of your best efforts. So let them stare, and stare back if you need to. You don't have anything to apologize for.

Odds are, they didn't notice! Everyone else is probably worrying about their own blinking and shoulder blade moving, and not noticing someone else.

Its okay if people wonder, just help them understand. People will always wonder about things, good and bad. Sometimes helping them understand will help them see it from a different view.

A lot of the time, in my experience, people are preoccupied with their own self-presentation. And honestly, if people do wonder why you do these things, I don't know if they will automatically make assumptions. Perhaps it will stop there, just a "wonder". If they are comfortable with you, or care enough, they'll ask you why you do so. And you can answer honestly. This sort of interaction will build their understand of you. People do all sorts of unique body movements! Don't be afraid to behave in the ways that feel the most natural to you. It is likely true that you are much more aware of your own unique behaviours than those around you.