Holy shit man you've got a shitstorm on your hands. Sounds like first your mom is going to hysterically scream at you, then cry for a couple of months, then hate you for years. You'll be lucky if she looks you in your eyes in the next three years.
and holy shit...I would feel so so fucking bad if I killed my dog...I fuckin' love that guy. I wouldn't be worried about my parents, I would be worried about the guilt and self-hatred that I would have to live with for the rest of my life. God damn, even thinking about it is bumming me out.
Guilt driven drug/alcohol benders would ensue.