My website is responsive when I resize the browser on desktop, but when I go on an actual mobile device, it isn't responsive

I want my website to be responsive on all platforms (especially mobile), not just on a desktop when resizing the browser window. This is the link to my website (so you can try it out for yourself): http://rtaneja.com

I have used the meta viewport tags in my that other similar threads say I should do, but nothing has worked.

Thanks