Why does this operation have margins？

[xcjcai]

var qr = new QRious({
background: '#FFFFFF',
foreground: '#FF0000',
level: 'L',
element: canvas,
value: qrData.data

                    });
                    qr.size=150

Why do some generated QR codes have margins

Excuse me, can't we ensure that the size of the generated QR code is consistent

[xcjcai]

Why are the generated QR codes of different sizes