Your math is correct, but your mechanics, perhaps deficient. As creatures grow larger in stature, weight increases disproportionately. Leg bones area would only grow as the square of height, so their legs would have to be thicker, just as an elephant’s legs are disproportionately thicker than a reindeer’s, even more so with a spider. I suppose they must have been quite spindly more like Kareem Abdul Jabbar than Refrigerator Perry.
That’s why I’m saying that the weight of this creature has to be wrong. He’s a spindle that can be easily broken.
I’m betting that he’s at least 700lbs.