How do I display three months in the event calendar view? I used calendar and views template module to create a calendar view for my Drupal 8 site, but the view returns only one month.  

I want to display three months. How can I get this?
It doesn't look like there isn't anything in the admin that will give you three months. I've implemented some similar solutions with custom calendars. 

There are a few ways that you could do this. I'm not going to get to far into the code, but just describe what I've done (I don't have a multiple-month example).

Method 1) Duplicate the monthly view and  alter the defaults in the contextual filter. Display these multiple blocks or feeds on a page.

Method 2) Create a custom node for displaying 3 months. Pass the contextual filter to the same view. Twig Tweak can handle passing arguments, though you may end up needing to do more preprocessing what Twig Tweak allows.