First, if you are unsure if Skydeck is backing up your contacts please log into Skydeck.com from a desktop or laptop computer (reset your password here if you need: https://skydeck.com/forgot_password). You should see your contacts (the first backup can take a while to show up). If your contacts have not shown up within 2 hours there are a few things that could be happening to cause your application not to backup.
Have you downloaded the Skydeck application to your phone? If not, you need the application to backup your contacts. Get the application from your phone application store or go directly to http://skydeck.com on your phone.
Did you login with the same phone number that you used to sign up? To access your account on Skydeck.com you must use the same phone number that you entered in the application when registering. To see what phone number the Skydeck application is backing up to go to Settings > Skydeck Account within the application.