Opt in email field not centered on different computers

So im configuring and making a squeeze page, however on widescreen monitors and mobile devices the opt in field is all the way to the left when it should be centered, i try dragging it but it only centers it for that particular monitor, halp?

my site: https://www.electricpineappleukuleles.com

https://www.ads-software.com/plugins/wp-lead-plus-free-squeeze-pages-creator/