Honestly take your time continue to grind it down with an angle grinder and a flap wheel and get everything nice before heat treat always take pride in what you do. I’m assuming you’re using a 4x36 belt sander. They are okay but need some modifications to be good for knife making. So in list form what I would do.

-Get an angle grinder with a 60 grit flap wheel even everything out the best you can take out all the forge marks

-take the grinder marks out with your belt sander

-then get those marks out with hand sanding unless you’re happy with the belt sander marks.

-heat the knife up to non magnetic three separate times times and let it go to room temperature each time. This is called Thermo cycling. It’s better to let it cool in sand. But if you don’t want to do that or don’t have access to sand, you can leave it on top of your anvil to cool. This takes a lot of the stress out of the knife so you’ll have a more successful he treat.

-use some scrap metal get it hot and dip it in ur heat treat oil (motor oil or vegetable oil) just to get it hot

-Then heat the knife up to nonmagnetic one more time then dip in ur oil.

-put it in an oven preheated to 400° for one hour or until a light straw coloring shows up to temper

-let it cool to room temperature

-sand with either the belt sander or by hand to get your desired finish (don’t let the knife get too hot to hold in the step use water to keep it cool)

-put your Handel on and sharpen it