Do you mean to say you've closed the contract yourself by marking "job completed successfully" and left a feedback for your client or is it you've clicked on "Submit work/Request payment" button?
It doesn't look like you marked the job as complete or closed it, but you clicked the button to Submit Work/Request Payment. There is no way to undo this, however, you can explain what happened to the client and resubmit the work later when it's ready. Note that if no actions are taken for 14 days, the payment will be released automatically from Escrow.
Check out this help article for more information about how fixed-price contracts work.