Don't get to discouraged dude... Learning how to call well with the mouth call takes some time!!!
I would suggest getting a few instructional DVD's on learning the mouth call and rent a few turkey hunting DVD's and watch those also...
And when it comes to practic. Practic often... I really dont think there is any such thing as to much practic when it comes to the mouth Diaphram!!!
For me it took me about 3 spring turkey season before I felt as thoe my calling sounded like I new what I was doing