Mobile site: page height is too long and not centered

I have a stacked website where each page is accessed by scrolling past the one above. For some reason the mobile website is only formatted correctly when you click on the link through Instagram, but on Safari and Chrome, the page height is longer than the phone’s screen and it cuts off the bottom 1/4 of the page. On Readymag, all of the pages’ designs are centered and it shows them in the correct formatting when I preview it. I’ve tried “fixing” the issue by making my pages’ designs shorter, but then when you click the link on Instagram, it shows the page as being too short for the screen and scrunched up to the top. Is there a way to fix this?

TLDR: Mobile site on Safari and Chrome cuts off bottom of all pages. Only Instagram allows mobile site to be viewed correctly. All pages are centered in Readymag and show the correct formatting when previewed. How can I fix this?