Less than 1% chance of spawn or respawn for scorpions. all you can do is keep walking around until you see it again, and make sure your net is out at all times so as not to spook it by bringing it out.
One thing you can do is get rid of all your trees and flowers, including digging out the stumps. It won't change the spawn rate but there will be fewer types spawning for the scorpion to compete with, since I suspect there is a limit to how many bugs can spawn at one time written into the game's code