Transmission fluid change?

I drive a 2004 Chevy Cavalier, 2.2L, A/T. I recently rear ended someone and as a result replaced my radiator, among other things. In the course of this, I lost a good deal of transmission fluid. I had refilled until it overflowed, then siphoned some out. Today I finally jacked my car up and put it on level jackstands. I removed a 7/16" hex that was supposedly a drain for the tranny fluid. From what I've read online, the only way to get the right level is to remove this bolt, and aim for a slow drip. When I removed this bolt, I lost a whopping 12 quarts, yes 3 gallons, of tranny fluid. The bolt was located near where the right front axle goes into the tranny, and was close to the engine oil plug. The capacity is only 7 quarts. What's going on here? I'm positive it was 12 quarts that drained. Now there is a slow drip coming out, but I can't imagine I'm at the capacity I should be at. Did I pull the wrong bolt maybe? Help please!

I need to know how do I know when I have enough fluid in my trans, after I change the filter on my car? My car do not have dip stick. Just a orange cap were you pour the fluid.