New Posts have bad layout and don’t use Single.php

Been trying to setup this blog and have it running for the most part however one thing I cannot figure out nor can I find a fix in the current discussions is for post layout. When I create a new post or even modify one of the templated ones I imported it messes up all the formatting. I’ve tried looking and editing the Single.php file. However that only affects posts that haven’t been tampered with on the import. All new posts or edited posts do not seem to use the single.php layout.