Button allignment

Hi, I have a problem. When I first made the app everything was fine, but after I turned off the computer and came back later, I downloaded the app again and now everything looks awful. The buttons that were at the top of the screen (“go back” and “post”) are now at the center of it. See for yourselves the screenshot below. Can someone help me? Does any of you know why I have this problem?

PS. This is not the first time this happens to me.