Hi,
Workflow does not store anything once it has finished execution.
It could be possible, your workflow has not finished it's execution before next execution.
Do you have a test activity to check workflow status before proceeding to execution of workflow.
If not, you can follow below steps to avoid workflow running if earlier run has not finished.
1) Define an option - 'isWorkflowRunning'.
2) In workflow, first check value of this option. If it's zero then proceed to execution of workflow activities. If not, then end your execution.
3) After test activity, have a JS, where you will set the value of this option variable as '1', indicating workflow is running.
4) At end of workflow execution, in your end activity, reset option variable value to '0'.
Thanks.