What's missing maybe is a good lamp for the workshop.
It makes things obvious if you have a reference.
See the light shining light underneath to show the error up.
It will make bad habits like nose diving off the ends with through shavings obvious
quickly
This is what happens without taking stopped shavings, resulting in a banana that pivots around in the middle when flipped over.
See Charlesworth demonstrating planing straight edges to fix this.
I suggest if your straight edge is not long as the bench, to make a pair of long parallel straight edges,
A pair because you can flip one over and see if both aren't following a curve, flipping one over will double any gap present.
Once you do that, then it might be an option to take a look at the bench or planing board and get it flat, be it planing it or shimming a door whatever makes sense for your bench.
Now plane down the timber where it is touching the straight reference, and don't try and plane into a low spot where the light is shining under.
You could even get a dark crayon and scribble it on the work surface to shine the high spots when the work is rubbed on it.
These are the high spots to remove with the plane, until all the timber is
laying down on the reference without any gaps.
See Charlesworth demonstrating the work pivoting from the ends on another video.
All the best
Tom