Maybe the costume just needs some time to work it's magic, you reassure yourself.
…Or maybe it has already been working without you noticing it. You try to clasp your fingers on your gloved hand, but alas, it still feels as if it were a human hand inside a mittens, and the lower torso still seems like very tight pants.
Suddenly, you feel something grow out of your butt in, with your spine extending itself, as if to accommodate the lower half of your taur costume. You even feel two new, skinny, digitigrade legs growing in, and your preexisting (fore)legs becoming slender and digitigrade as well, eventually making you stand on four digitigrade legs (you must admit that standing on tiptoes feels strange, but the legs somehow manages to hold up your body weight, despite having to carry an extra upper torso), and the spine extending itself ultimately into the tail, now wagging viciously. Turning your head to look behind, you notice the lower torso and hindquarters standing up on your hind legs, and as you try to touch your lower body with your gloved hands, you can feel the hand run across your forelegs and lower body, and then grab and caress your own tail (you have to lean your upper torso a bit to reach that far behind). The lower portion of the costume did animate itself after all!
Knowing that you now stand on four legs, you try to sit on your hindquarters, and turn back to see your furry butt parked on the ground, the tail still wagging. Afterwards, you bent your forelegs to lay your lower torso onto the ground, it resembling a pose dogs adopt when they are at rest. You try to wiggle your toes, and find yourself wiggling the toes on all four paws. Maybe it's best to remain in this resting pose until the transformation completes itself.
The same magic crept up your waist and to your upper torso, also sticking the upper portion of the costume to yourself, and your hands merge with the paw gloves to form handpaws that still have opposable thumbs but with a claw at the end of each finger and soft pads cushioning them. Intrigued, you push one of these pads with your thumb, and feel it as if it were a part of you. As you ran your hands across your upper torso you also feel the presence of your hands. The costume had completely melded itself into your skin, but there's just one part that hasn't changed yet…
The head!
Your face abruptly stretches forwards, forcing your eyes shut; fur growing from everywhere, your mouth elongating into a whiskered muzzle, your ears migrating to the top of your head, and your nose becoming wet and much, much more acute than before. You can smell everything around you now, which, given the current situation, isn't much more than the scent of fabric and fake(?) fur. Perhaps that nose could be put into good use once you exit the costume store?
As you reopen your eyes, you notice that you see fewer colours, but your field of vision is slightly wider and your vision is a little more acute.
Looking inti a mirror and try to take note of your new body: a slender, muscular greyhound taur.
There is no time to spare. Greyhounds are born to run, and you are no exception. You quickly stand up from your lying posture, looking forward to exercising the newfound legs of yours.