Not bad,...I think I would figure out a way to make a template and/or mark the tape so that your stamp was a bit more consistent and higher on the call.
I suspect you are rocking the stamp when you push down, and that is what is causing the lines to show. You might try shaving the stamp around the edges so that it is more difficult for the edges of the stamp to make contact when you stamp the tape, too. ...Might try a different color ink, as well. The black is a bit bland. Other than that, it looks great!