I don't know that your slide foot is a massive problem, some of the balls you delivered in the video were being sent outward, towards the gutter, in which case an angled slide foot wouldn't be a problem. It's difficult to tell without seeing your whole approach, but I would guess that that much foot angle would be created by an approach during which you drift left and then correct for the drift during your slide. Your slide also looks a little short, causing your trailing leg to catch it up. I would suggest looking at your whole approach, and trying to see where your steps are taking you, I find it useful, if I'm drifting, to try and walk to the right, which will take me straighter.
Getting lower at the foul line as the other response has suggested, will help with keeping your fingers under the ball.
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Reporting from England