Works fine for me:

$ perl -e '
>    $nfc_amt = 114;
>    print "NFC_AMT before adding zeroes: $nfc_amt\n";
>    $nfc_amt = sprintf("%07d", $nfc_amt);
>    print "NFC_AMT after adding zeroes: $nfc_amt\n";
> '
NFC_AMT before adding zeroes: 114
NFC_AMT after adding zeroes: 0000114
[download]

How are you setting $nfc_amt in the first place?