I'd duplicate the layer with the animated mask on it and use it as an alpha matte for your clean plate.
Unless you shot this all in profile, the mask around the dart will take part of your head, too. Do you also have a good "before the dart hits" clean plate of you, from a matching angle?
The screenshot helps. It shows that you've got a few things wrong.
Put the clean plate layer under the layer with you. And turn on its visibility (eyeball) switch so that it's visible.
Your mask mode is set to None, which means that the mask isn't doing any masking. Change that.
When you have the clean plate under your other layer, and you have a functioning mask cutting a hole through your layer, your clean plate can show through that hole from underneath.
This is all very basic compositing and After Effects stuff, so I recommend that you begin at the beginning: