Assuming that HTTPS is working okay which it seems to be:
Make sure you redirect HTTP to HTTPS.
Make sure your sitemap, if you have one, is using HTTPS.
If you have made this change in the past few months, please know that the changes will take quite a while to be relfected in the SERPs. Google keys their database off of a couple of things. One of the principle keys is the URL. This is the full URL. In otherwords, for your site, HTTPS and HTTP are two different URLs. As Google refetches your pages, with the redirect, Google will replace the HTTP URL with the HTTPS URL.
It is that simple.
Google will have to fetch each and every page in order for it to change in the SERPs. This takes time depending upon how fresh your site/pages is/are and the size of your site. Keep in mind that search engines are not real-time and that Google can fetch all the URLs within it's index within about 10 months. This means that it will take months, but not likely more than 10 months.
If you have dome everything right, then it is just a matter of time and being patient.