Canvas is by default an inline element. And inline elements have a white space underneath them, for the descenders, parts of the letter like "g" or "y" that are below the baseline.

So, just set your canvas to block:

canvas.style.display = 'block';

Or with CSS.

And the meta viewport is a comma-separated list:

<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=0">