i'm somewhat of an artist myself, not professionally though
but first thing i noticed was that it had 7 tenticles. i'm sure you intended to do that though, unless you started drawing and found out later that you couldn't fit 8 without completely jacking it up or having to start over, lol, i've done things like that before when i used to draw. other than that, can't really tell what little mistakes you are referring to
how big is the real drawing btw?
edit: sorry someone already pointed out the legs