Text box way too big

I’m using Dream Home theme, which I find to be really rubbish compared to some I’ve used.

I’ve created a contact form plugin as well as enabled comments.

The comments box is way too big, and it overlaps with the other side of the page. The contact box is also too big for its side.

Any way of fixing this- and before anyone guesses, I’m no expert on WordPress so I don’t understand anything advanced. Go easy on me.