You’ve used a fieldset, which has a default border, so:
The answer is in the question, with CSS grid
Put all your checkboxes in a div with class checkbox-grid and add a grid:
You won’t like how the layout looks with that, see below:
In your labels, you have an input and some text. It would make sense to wrap the text with a
<span>, so the structure is
So now you can style those as you like, increase the distance with margins/paddings or rearrange the elements with flex.