Uhh... I just find it ironic that us Law Enforcement types get bashed as trigger-happy jack-booted thugs.
I have handled many a "bat call" at night when Animal Control won't or can't come out and someone is absolutely terrified of the some poor winged rodent that got trapped in their house.
Want to know a little secret? The bat doesn't want to be stuck in your house any more than you want to get it out.
Next time a bat gets trapped in your domicile, open some windows (take the screens off if they are up) and open your doors. The bat will usually be on the wall or ceiling. Give the wall next to the bat a tap with a broom or a mop (or a baton, but be gentle on the sheetrock). The bat will start flying, and through the miracles of the bat's echolocation (natural sonar), the bat will usually find its way back outside within a minute or so.This works almost every time unless the bat is very sick.
Also, if the bat is stationary on the ground it is probably sick. If it is a sick bat, it is probably infected with rabies, which can be spread by fluid contact with unbroken skin. If that is the case, let Animal Control Officers get it. That is why you pay taxes (whether you agree with paying taxes or not). Your best bet is to contain it. Drop a wastebasket over it. If you have a compelling need to get it out of your residence and Animal Control can't get there any time soon, slide a piece of cardboard under the upside down can and carefully carry the whole unit outside.
Regardless of what kind of load you were using, discharging a firearm inside of the house was not a very smart thing to do under those circumstances, and the bat posed no direct harm to you. It did not need to be killed.