JS Canvas – My clicked positions work on desktop, but aren’t working properly on touchscreens

I’m doing a project, learning canvas.
My basic operations work (dragging mouse over the canvas to draw, clearing)
but when I switch to touch, it draws offset, like diagonally down and right from where im clicking

here’s my codepen: https://codepen.io/Dolevy97/pen/ExzwaLe

and the relevant lines of code:

function onMove(ev) {
    if (!gIsDrawing) return

    gCtx.fillStyle = gBackgroundColor
    gCtx.strokeStyle = gShape.color
    gCtx.lineWidth = gShape.size

    const pos = getEvPos(ev)
    //* Calc the delta, the diff we moved
    const dx = pos.x - gPrevPos.x
    const dy = pos.y - gPrevPos.y
    move(dx, dy)
    gCtx.fillStyle = gBackgroundColor

    if (gShape.shape === 'pen') {
        gCtx.lineTo(pos.x, pos.y)
        gCtx.stroke()
    } else if (gShape.shape === 'square') {
        gCtx.strokeRect(pos.x, pos.y, 50, 50)
        gCtx.fillRect(pos.x, pos.y, 50, 50)
    } else if (gShape.shape === 'triangle') {
        gCtx.moveTo(pos.x, pos.y)
        gCtx.lineTo(pos.x + 80, pos.y + 80)
        gCtx.lineTo(pos.x - 20, pos.y + 100)
        gCtx.closePath()
        gCtx.fill()
        gCtx.stroke()
    } else if (gShape.shape === 'circle') {
        gCtx.beginPath()
        gCtx.arc(pos.x, pos.y, gShape.size * 10, 0, Math.PI * 2)
        gCtx.fill()
        gCtx.stroke()
    }

    //* Save the last pos, we remember where we`ve been and move accordingly
    gPrevPos = pos
}

function getEvPos(ev) {

    let pos = {
        x: ev.offsetX,
        y: ev.offsetY,
    }

    if (TOUCH_EVS.includes(ev.type)) {
        ev.preventDefault()
        ev = ev.changedTouches[0]
        pos = {
            x: ev.pageX - ev.target.offsetLeft - ev.target.clientLeft,
            y: ev.pageY - ev.target.offsetTop - ev.target.clientTop
        }
    }

    return pos
}

I can’t understand what’s not working because it seems that it works for others with the same getEvPos.
Thank you!

I tried playing around with it, but to my understanding, the calculations in getEvPos are constant and shouldn’t be touched. So it’s probably something in my ‘onMove’