Workflow firing at wrong time

I have created a workflow to fire when a form is edited (Start workflow automatically when an item is changed) by a user who is not the Assigned user for this form:

'If Current Item:Modified By not equals Current Item:Assigned To Email Current Item:Assigned To'

Is this incorrect, as the workflow is firing when the form is edited by the assigned user which is not what I have requested ... Also, this workflow is firing when a 'New Form' is filled out which it should not, as I have selected the start option as 'Start workflow automatically when an item is changed'.

Do I need to delete the workflow and create again? Or is there something I need to do/undo?

Thank you for your time,

Janice :)