Well, now since its all electronic you don't need to submit your I-94 anymore. Even if you try to hand over your I-94 they won't accept it. They scan your passport before departure and submit it to DHS or responsible parties. That's how they will record your departure.

This happened to me a few years ago. I tried to hand my I94 but they didn't accept it. I was worried but everything went fine. So no need to stress about it.