Head over to My Account to link a credit card. You'll notice that your current subscription is in Trialing mode until you add your credit card and the charge is successful.
If this is your only trialing subscription, adding a card will instantly activate your account and charge the first months subscription.
If you have multiple trialing subscriptions, you'll need to select the subscription you're wanting to activate now:
Once you've activated your subscription, don't forget to head back to your Pre-Launch or Crowdfunding settings to set your page live.