I have what I feel is a very basic question but after building a form and re-checking everything 5 times I can't figure it out...

I have build a form which allows people to register for an online ticket (nothing too technical!). 

At the start when a friend was reviewing (on her mobile) it autosized to fit the screen... now that I'm done it no longer resizes and the form is too big (font and pic). I've checked to see that everything is on 'auto' and I THINK I have everything but obviously not.... 

Can someone point me in the right direction?

Thanks in advance,

Jenny