First of all, your document is stored as .docx which means it undergoes translation from/to internal format to alien format when you save and open the file. This has the effect to damage cumulatively the document structure because there is no one-to-one correspondence between format features. List and chapter numbering is one of the known problematic issues.
Second, your document is a real mess with a bad mixture of (rare) styling and (a tremendous use of) direct formatting.
You have played with Tools
>Chapter Numbering
settings without understanding all the implications: you replaced Heading 1 usage with custom h1 paragraph style So, you definitely don’t double-click on Heading 1 but on h1. You messed up the chapter auto-numbering feature making impossible to generate a TOC. In addition, you disabled internal chapter numbering for level 1 (Heading 1) and replaced this by a custom list style WWW8Num1 which is a clear indication of alien format corruption.
Regarding your “alignment” issue: your chapter title is void (there is nothing after the tabulation) but the tabulation is taken into account to compute the width of the paragraph before centring it. No tab stop has been defined in your h1 paragraph style; therefore Writer uses the default evenly spaced stops (spaced apart 1.27cm unless you customised them). Since THREE is wider than TWO, you end up one tab stop farther and this gives you a wider heading.
Fix: modify your WWW8Num1 list style to request “nothing” after the number. But the real fix would be to include the chapter title in the heading and use a New Line after the number. This requires that you revert to standard Tools
>Chapter Numbering
configuration and probably you save your document in native format i.e. .odt.
Your document is presently totally unstructured. You should start by reading the Writer Guide and also Bruce Byfield’s excellent book available at the same location. There are too many things to say about your faulty usage of Writer. I’d recommend your restart from scratch methodically and rigorously avoiding absolutely any direct formatting.
If you know what your book should look like, it is easy to deduce which styles to use and how to configure them. Understand first built-in styles (with limited user customisation) before trying to design your own.
And don’t, don’t, don’t mix list numbering with chapter numbering. They should be kept separate unless you really want things going awry.