It's uncommon that a regular key would get stuck in a lock like that. When this happens it's usually due to a back-cut key or a bump key that has the ramps cut too steep. In any case, most likely you have a tumbler that is jammed and won't lift to allow the removal of the key, It could be scratched up from being picked a lot, grit in the lock, or lack of lube. Or lock gremlins.
This is the point at which I would recommend to most people that they call a locksmith, and/or replace the lock. If calling a locksmith isn't an option, or if you're simply determined to get yourself in even deeper, continue reading...
Get a can of a good quality lock lube, with the little straw attachment. Try to squirt a bit of lube into the keyway along the sides of the key. Then gently rock the bow of the key up and down a bit to try to loosen things up and spread the lube around. After rocking up and down for a minute or so, try gently wiggling the key in and out of the lock while continuing the up and down movement. Don't be forceful. You're trying to free it up, not jam it worse. Be patient, and try this for a minute or so. If the key still won't come out, move to the next step.
Get a long, thin shim. Something like a Weiser Shim (pictured below) or a Peterson mini-knife. You'll need to cut a corner off the tip of the shim so the front edge is around 45 degrees, so it's like the ramp on the front of the key. You're going to try to use the angled tip of the shim to lift the pins. The next instructions assume your schlage deadbolt has the "C" keyway, which is the standard keyway Schlage uses on household locks in the US and Canada.
On the right side of the keyway there is a single ward that protrudes into the keyway. Hold the shim level to the ground (the long axis of the shim should be parallel to the horizon, like in the picture below). Make sure the slanted edge you cut on the tip is facing upwards. Insert it right above the ward. You'll probably need to keep the bottom edge of the shim resting on the ward to use it as a guide. Slowly insert the shim into the lock; you may need to wiggle it up and down slightly as you get to each pin in order to lift it. You'll probably encounter more resistance when you get to the stuck pin. When this happens don't force it, but continue to wiggle the shim up and down a bit to try to free the pin. If needed you can gently (VERY gently) pry with the shim, using it as a lever with the ward as the fulcrum to pry against. If you're able to fully insert the shim as far as a key, you should be able to remove the key at this point.
If you're not able to remove the key, remove the shim and try again on the left side of the key. There are two longitudinal grooves in the left side of the key. Insert it along the upper groove using the same procedure as you did on the other side. This will insert the shim slightly higher into the lock, and allow you to lift the pins even higher that you did on the other side of the keyway. Continue until the shim is fully inserted or you're able to remove the key.
If this doesn't work, hide all evidence that you tried to fix it yourself and call a locksmith like you probably should have done in the first place. Good luck. I hope this helps you out.
