Formatting word doc

I've written a book and uploaded it to Kindle. I have two books available already and formatted them without issue. This time Kindle Preview looked fine. When the book went live, I checked it on my smartphone and there were spaces in sentences which were not on the preview. I contacted Kindle and they said I had used hard retus. If I ^9 to expose the paragraphs, and then soft retu them I still have the issue of justify. The sentences with few words go at each end of the page! Can anyone advise me how to resolve this please?