If you don't know your job number, check out this knowledge base article on checking the status of your jobs
Use the scancel command:
[user@rush:~]$ scancel --help
Usage: scancel [OPTIONS] [job_id[_array_id][.step_id]]
To cancel a job:
scancel [jobid]
To cancel all of your jobs:
scancel -u <userid>
To cancel all of your jobs on a specific partition:
scancel -u <userid> -p <partition>
To cancel all of your jobs using a specific qos:
scancel -u <userid> -q <qos>
To cancel all of your jobs on a specific PI cluster:
scancel -M <cluster> -u <userid>
To cancel a specific job on a PI cluster:
scancel -M <cluster> <jobid>