I can align the text to the center, and to the right. When I align the text to the left, the edit view will appear correct then when I go to preview the page the text is centered. See attached images.
I have copied the text into Textedit as plain text and then pasted it into a new text box and the format aligned left will appear centered.
Which theme are you using? Some - for example, Paramount from Michael David Design - may have their alignment set in the theme settings which will need to be overridden.