When Google ranks you on the search engine results page it considers the indexed pages, not necessarily your current website. They may differ for a while. The shorter the better but cannot avoid such situation as you don’t control the process 100%. Guess you’ve already submitted your website to Google using the Fetch as Google functionality or by submitting your website’s sitemap.xml file, also implemented the proper Redirect 301 instructions. The Google bots crawl your website and help index your HTTPS version as soon as possible, also replace the old HTTP pages with the new HTTPS pages in the Google index. When this happens, your new HTTPS pages start ranking on Google. Until then, it’s perfectly normal for Google to take some time to recrawl your website and index the new versions of your pages. Switching from HTTP to HTTPS is a significant change on your site and when it is doubled by a significant number of pages on your website, it is normal to take some time. A lot of URLs drop out fairly quickly as Google sees them on the HTTPS version but for the rest it might take a while.
Important, you don’t need to force the process, you don’t need to manually tweak to make the HTTP pages go away. It is simply the normal crawling and indexing process. And, with the Redirect 301 in place, people land on the right pages. Google will soon consider the new HTTPS pages and everything will be fine. Don’t forget to add your HTTPS version in Search Console, dropping in impressions in HTTP will be backed up by increasing in impressions in the HTTPS version.