It looks like what the instructions call "the white wire coming into the fixture" is not in the picture. Make sure you know which one it is. It comes in with a black wire that goes to the switch. There's a different black wire that comes out of the switch and goes to the ballast; that's the black wire in the picture.

So just follow the directions; don't overthink it.

Cut all five wires off of the ballast.

Connect the black wire that you just cut to the two red wires that you just cut. Don't do anything else with black wires or red wires.

Connect the white wire coming into the fixture to the white wire that you just cut (it might already be connected) and to the blue wire that you just cut. Don't do anything else with white wires or the blue wire.

Close up the fixture. You're done.

It looks like what the instructions call "the white wire coming into the fixture" is not in the picture. Make sure you know which one it is. It comes in with a black wire that goes to the switch. There's a different black wire that comes out of the switch and goes to the ballast; that's the black wire in the picture.

So just follow the directions; don't overthink it.

Cut all five wires off of the ballast.

Connect the black wire that you just cut to the two red wires that you just cut. Don't do anything else with black wires or red wires.

Connect the white wire coming into the fixture to the white wire that you just cut (it's almost certainly already connected) and to the blue wire that you just cut. Don't do anything else with white wires or the blue wire.

Close up the fixture. You're done.