New paragraph, why is it double spaced?

Dear Amber, First I want to thank you for your patient help and diligence with my problem. I slept on it and came up with a fix. I can copy/paste from my PDF onto the Scriviner editor. In order to remove the double carriage spacing I put the cursor on the sentence before the double spacing, hit delete twice and that brings the next (double spaced) sentence up. Then, I hit the tab control until the sentence ends up below… not double spaced. Then, I simply put the cursor in front of that sentence and hit tab once more and it indents just as I like it. I know that sounds tedious, but it is much better than retyping the entire novel. Now, I can go through this process fairly easily and then compile and send the book over to documents for e-pub. Hopefully this will eliminate the file failure causing the book to be rejected.
I do have one more question. I like the book to be aligned both left and right margin. But, that means that some shorter sentences get spread out across the line. If I highlight that one particular sentence, then use the icon to align it to left only, the rest of the chapter gets aligned left, not left/right. Is there a method where I can keep the shorter sentences from becoming widely spaced across the line and still retain the left/right margin? Once again, thank you so much. Rad