i am looking for screaming men for couple of days, and finally i found this, and i think it is very natural. most of "screaming men" or "dying men" sound like they are throwing up. so i think that your scream is great and you didnt fail. its just the nature of your voice.
However for recording purposes WAV is good. Because it's easy to read and write - it's light on the CPU making it possible to playback and record multitrack recordings (for exampe in Ardour, a free-and-opensource DAW). Using FLACs instead makes things stutter and block. FLAC is not for multitrack ;-)
I needed a nice clean growl and put a limiter on it to transform your cute dog into a bad dog :) I would like to thank you for the effort and give the dog a bone! It's somewhere in the middle of the track: http://soundcloud.com/mood-morpher/guilty