Why have you got 5 at the end of your short text and full text? Do you have multiple show more/show less on your page?
If not, then simply take off the 5 and make sure that you have followed this tutorial correctly.
https://support.wix.com/en/article/corvid-tutorial-creating-a-show-more-link
Plus, when you say collapsed page body, you can collapse and expand a element with the collapse and expand functions.
https://www.wix.com/corvid/reference/$w.CollapsedMixin.html