To get a working machine that will produce accurate parts first the machine needs to be set up correctly so for the moment just forget the G-code side and let us make sure the machine is set up correctly.

So we need to know the control software your using and the settings you have entered for starters, there will be other info that will be needed but let's start with this first.

Also just to eliminate any chance of mechanical issues just check it's not falling apart and the Axis move freely when NOT under power. There should be resistance but not really Stiff. There should also be NO or very little movement before the motors or screws turn if you grab the axis and rock it back n forth.

We will get you cutting and there should be no reason why you cannot cut plywood or any wood for that matter to a reasonably good standard even with a cheap machine like this.
But it may take several posts and the more info you can give us the quicker it will be. A good way is to take nice clear pics of the screens or if we ask about electrics do the same.