Responsive theme not seeming too responsive

I am experimenting with a free wordpress theme called Mantra. Surprisingly, I have figured out how to do a few things. But even though it is supposedly a responsive theme, it looks different on my phone. I have made the header smaller and sharper, changed my background photo and moved the title to center but these changes are not showing up on my phone. Plus a test post that I deleted is still showing up on my phone (but not on my notebook). I know this isn’t a premium wpmudev theme but can anyone give me any suggestions? I was just starting to get a shred of confidence that I might be able to create this site. You guys keep saving me…hoping for another catch. :slight_smile: