twenty twelve not responsive on iPhone

I started making this site myself on a course.. and I’m not that techy – in fact not at all techy! Do you think I should go to a developer? I’m keen to keep the site ‘my own’ but don’t really understand the css stuff. I suspect that I should get a premium theme, as someone told me it would be more user friendly – is that right? Sorry – 2 separate issues really.. but any help appreciated.
https://www.helenacklam.com