Hi Chris, that grain filling looks fine how you sanded it back. I can't remember seeing a guide on the forum to the procedure.
The idea is that you sand it back till you see all the grain. You can see the area closer to the larger holes needs more sanding.
If you think the mix is too runny add more timbermate to the mix.
I generally sand to about 240 grit before applying it, then lightly sand back the timbermate 240 and 320 grits
Is that ebony timbermate ?
This is what DB said about grain filling on Ralphiles TLA-1 build diary below:
My preferred method is to mix the TM with water until it just maintains a peak when you lift the spatula out of the mix, slightly thicker than cream I guess.
On flat surfaces I use a rubber sqeegee and force it in across the grain.
Let it set for an hour and sand back with 320 grit and re apply if needed.
Have a play around, see which method works best for you is probably the best advice I can give...