I suggest removing tags width, heightand alignfrom the canvas. Instead, add a style area to your html and define a css style for the canvas:
<style>
canvas {
padding-left: 0;
padding-right: 0;
margin-left: auto;
margin-right: auto;
display: block;
width: 320px;
height: 480px;
}
</style>
Your canvas will look like this:
<canvas id="Shooter">
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