https://domain works fine but http://domain show "Not secure"

We recently attached a domain we own to our SquareSpace site and we obviously have a working SSL cert at https://teamchase.life as indicated by the browser lock icon. We also ran an SSL checker just to be sure. However, if a user enters http://teamchase.life in either Chrome or Edge you get the Not Secure warning. Squarespace is a bit different than other sites I manage where I just redirect http to https in the .htaccess with a stanza like 

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTPS} !=on [NC]
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R=301,L]
</IfModule>

How can I do that with a SquareSpace site? I couldn't find a setting to ensure that http is redirected to https.

Thanks for any advice

Hi Paul and Delsol,

I'm experiencing a similar problem!

I already had HSTS enabled. But the issue I'm experiencing is when I try to enter my portfolio with my bought domain (via Squarespace, https://www.emtemark.com/) on my computer laptop at work. I get the message "not secure" on chrome and safari. However, I can access the portfolio by going via the longer/original link (https://emtemark.ssquarespace.com/).

But strangely, when I try the same at home with my work computer it works fine to access my portfolio on the bought domain... 

Is this a bug since I entered my portfolio on various occasion on my work computer and I just need to clear cache or so? (will need to try it next time in office...)

thanks!