Now, just to state the obvious from my side, the grit on the sandpaper and stick looks waaaaayyyy to course compared to what I use... Fine grade paper that can be used wet or dry is what I have on my bench...
Ive never used anything like what Wojteks pics show, I would think the scratchs in the plastic would be severe, and I can see some of those small scratches in ur pics H...
Also, remember, u dont want to, or atleast try to avoid sanding off or covering up any of the panel lines that want to stay visible... Truth time will be when u get ur first coat of paint on the seams, then u'll truely see just how well the sanded putty looks.... Ive had to go back several times on a couple of seams Ive done after a first coat of paint and sand more, then paint and then sand and paint again...
My least favorite part of model building....