It could be a number of things. I see that you have a very new rezz date- if you're an alt or returning to
SL, you might want to mention in your profile that you're not a newbie. Some clubgoers do not like girls with newbie avatars.
What language is spoken by the majority of the people who go to the club? What country or countries are they from? If your primary language is English and the majority of people who go to the club primarily speak, say, Spanish, the language barrier could prevent you from getting tips. Also, people from certain countries (and to avoid a forum war, I won't say which ones) have a reputation in the club world for being poor tippers. If your club is catering to a clientele that does not tip well, you'll have a hard time making money.
How are you interacting with the customers? Are you friendly to everyone, or do you only talk to people with payment info on file? Do you engage people in conversation? Do you rely on saying things like "tip me to strip me"? Do you emote well? Do you use a lot of chatspeak ("hi how r u hunnie lol")?
Without seeing you in the club, it's hard to say what you're doing "wrong". However, you might want to take a half hour or so to see what the top earning girls are doing. You can learn quite a bit through quiet observation.