Sitemaps are not the be all - end all that most people think they are. Let me set the record straight.
From this answer: sitemap.xml for a website with forum
As far as sitemaps, they are intended only to inform search engines of
what pages your site may have. Generally speaking, sitemaps benefit
those sites that are very large, cannot or do not link all pages
directly, have a barrier such as a pay-wall or login, or where not all
pages can be found easily via the linking method used.
Search engines generally prefer to spider any site the old fashioned
way. However, if a sitemap is supplied, search engines will compare
the sitemap to the pages they can already capture without a sitemap.
If the two lists are the same or end up being the same, search engines
will prefer to spider and index any site by following links. Part of
the reason for this is rather simple. Links signal importance and
sitemaps remove this signal. It is quite common that other than
reading the sitemap for comparison, search engines will ignore a
sitemap. One common exception is for very large sites.
Having said that, for a smaller site, the sitemap is largely ignored. But do not let that frustrate you. It should not.
What is important is that your links are easy to follow, your site has quality content, and that your site performs well in the SERPs. Google will index a site in it's own time. You cannot hurry Google up. Do not try. It makes the big G mad when you do.
Another interesting phenomenon is that Google does not always the entire site leaving some pages on the table. For example, of my nearly 700,000 pages, about 32,000 are not indexed and will not be quickly. This is true for smaller sites too. What encourages Google to index more pages is fresh content. Keep adding content and improving older content. As well, SERP performance is another factor. Google will index an entire site if it is a top performer and that takes time- trust me.
Here is the good news. If you are willing to accept what is true, then you can deal with it by creating the best site available and anyone can create a top performing site, but it takes time. No new site come out of the gate a winner. You have to run the field for a while to know how to compete and what races you should run and what tracks are in your favor.
My immediate advice is to create great content, making the site simple to use and index, and work on performing well in the SERPs. Do not worry about what you cannot control and work on what you can control.