I am a fitness director in a gym and a fitness management consultant at tons of gyms. Needless to say the gym game is comes easy to me and I have had a lot of success with it. Your opener is great because it is non threatening and playful. The neg is perfect! I would have added just a touch more.

After she showed you the exercise I would said "now I am going to show you one"

This will allow you to move the target and get her following you (hopefully back to your place eventually)

Keep in mind that if she is still talking to you then attraction is obviously there.

Now pick any exercise for the lats, posterior deltoids, rhomboids. Show her an example of how to do it. After your set spot her on hers. Explain that these are muscles that women have a harder time identifying with and place your hand on the area and have her focus there. (Kino) If she is digging your touch you will definitely know.

If all is still giggly and well then you can smell her hair and whisper something along the lines of (Mystery) "I am trying so hard not to kiss you right now"

With enough sexual tension and kino you are probably not getting action on the spot but as an after gym cool down. I can tell you from personal experience that this works. I think secretly every time a chick sweats she starts thinking about fucking. It's like there whole system get's primed. Cute girls at the gym are either wondering if they looks sexy or thinking about how sexy they are going to look. Either way they are thinking about feeling sexy. Just try the exact same open and finish like this at another gym... when you get her home just make sure all the banging doesn't make her go over 80% of her maximal heart rate;That will cause her system to go catabolic and completely waste her workout : P