I’m going to say something that eventually you want to stop doing.
Push your mouthpiece farther onto the cork, significantly. By a lot.
It’s easier to bring a pitch down than to bring it up, so even if your low notes become a little (not a lot) sharp, that’s probably okay for now.
If you went too far and everything becomes sharp you can adjust it. You can check if you are in tune with a tuner/tuner app.
I would say it’s somewhat unlikely that many people play sharp when they first start to play. You should realize that probably not every note will be in tune for at least the first few months, but it would help to be somewhat close.
It’s very easy to be quite flat on all the notes you play when you start. And most sax players probably don’t assume you should push the mouthpiece on too far. But it’s probably better to be playing closer to in tune than getting used to playing really flat.
Your ear will pick up how you play.
You can also listen to more music played by good musicians to have a better sense of what playing in tune sounds like.
And as you become better at the saxophone, you’ll adjust where the mouthpiece is so you can play in tune.