I'm barely a beginner myself but A: I wanted to say that's a really cool idea and B: being a beginner your hand will affect the shape. I'd try tactically moistening and letting the work dry into the intended shape. Actually with cotton you'd probably want to make sure it gets all stretched out so it won't get droopy over time. You could also stagger the increase and decrease spots that they are more evenly all around the work, rather than all in the same vertical line.
Also just as a note, be sure to use non-heating lamps.