This means you are bending too much, I’d say you are using too much force. It’s cliche, but true, you really need to relax 🙂 Try to go really slowly down to the bend. Using as little breath as possible. You can bend a few times on the 2 hole to get the idea, of going slowly and generating more control. Then go back to the 3 hole and try again.
if you get this going really nicely it should almost sound like a slide guitar, then yo can use an app or a digital tuner like Udo suggests, to check for accuracy on each semitone!