Dear All
thank you for your help.
FYI and other candidates in the future - i was not posed a problem. I just sent in the only receipt that the bank gave me back, after keeping a coloured photocopy of the same. My name is not in the rejected candidates list so it is confirmed that it was not a serious issue, even though i will be careful next time.
Moreover, no challan form is resubmitted at the time of css papers or interview. I have confirmed that much from FPSC.
Best of luck to all.
remember me in your prayers also.