@Annette, If you are viewing your site in the latest Google Chrome browser it might be the cause of your alignment issues. I have had issues just off late when testing on it. All the other browsers works as should.
If not the browser have you physically aligned (page elements like images, content containers, etc…) your tablet and mobile layouts after hitting the “+” in the Sparkle canvas? When your hit “+” Sparkle will proportionately reduce your site to the smaller device but you have to go in and make sure everything presents well for the smaller device.