If you haven't figured this out yet, this is actually a simple one. At times the Wix Editor gets hung up and I have no choice but to save what I have (if it didn't already auto-save) and then refresh the entire page (to where it refreshes your editor altogether). You should now be able to Preview your page.
Thanks for your reply. I tried to do as you suggested, unfortunately as soon as I click on 'preview' after I refreshed, It open the preview, but the page is cropped and It doesn't show everything, do you know any other way I can fix that?