I’m guessing all of the card. variables are blank correct? Unless you’re using an assign before them to create an array those are always going to be blank.
As suggested above I would just use the jekyll-seo-tag plugin as you get all of those meta tags “for free.” The plugin had been widely tested and works very well with little to no config on your part.
Otherwise I would suggest changing card to post so you end up with post.title, post.url, etc.