My necktie t-shirt came out differently because I made bigger ruffles, used a t-shirt with a shorter V neckline (I think hers may have been a scoop neck), and may have used a wider tie. I stitched both sides down (and did some fancy work to stitch under the ruffles and hide my stitch lines), which flattened the folds. McKell simply stitched straight down the middle, making her ruffle tie fluffier.
Although it was not mentioned in the tutorial, I cut open my tie (where it’s stitched closed) and removed the thick interfacing, making the material easier to fold and lay down. Different ties have different consistencies. Some ties need their interfacing removed, and others are thin enough with the interfacing; feel the tie before making a decision to remove its insides.