How about determining the script name like this?

#!/bin/bash

SCRIPT_NAME=$(basename "$0")
dupe_script=$(ps -ef | grep "$SCRIPT_NAME" | grep -v grep | wc -l | xargs)

if [ ${dupe_script} -gt 2 ]; then
    echo -e "The $SCRIPT_NAME script was already running!"
    exit 0
fi

consider looking at "pgrep", one for "-c" to count the pids and two for -f "for full path", three -u for uid running, and execute with fqfn so that the script is "/path/to/script/runtime.sh" not "runtime.sh". Now you can run multiple scripts of the same name and not get conflicts between them (eg, ~/bin/cron.sh and ~/test/cron.sh) and other user's cron.sh won't clash, or when you are editing cron.sh (eg, "emacs cron.sh")

https://man7.org/linux/man-pages/man1/pgrep.1.html

just found this - pgrep does the job (just be careful with cron and using different shells in script and cron ;)

function check_script_running () {
        for pid in $(pgrep -f $(basename $0))
        do
            if [ $pid != $$ ] 
            then
                echo "[$(date)] : $(basename $0) : Process is already running with PID $pid"
                exit 1
            else
              echo "Running with PID $pid"
            fi
        done
}