I think you need to get her number, but really you are thinking too much about this one girl, and if you do that too much you will give off a scent of desperation to her, and no girl will date a guy they think is desperate. My suggestion, talk to some other girls in the gym. If she sees you talking to other girls she'll have more interest in you. Girls don't want to date the single guy, they want the guy that can have any girl he wants, so talk to some hotties. This is also good for 2 reasons, you could get 2 phone numbers rather than just 1