You have to design your scripts to be stoppable (or write a script to kill it). There is no UI for doing so. I killed the script for you.
I do see the index.sh in your cgi-bin folder, and looking at the code, visiting index.sh?action=stop should trigger it to kill your process.
The good news is based on the past few hours of usage, your script wasn't even that heavy and shouldn't have a problem with memory usage even if you need it to run continuously.