OK:
1st Download stock RUU
2nd Try to flash the RUU 1st time (it will flash your Bootloader but will fail later becuz ur bootloader is still unlocked)
3rd relock ur bootloader (u can do this with several SXL toolkits (i prefer: http://xdaforums.com/showthread.php?t=1865265 )
4rd ~~ now u should be able to flash the stock RUU ~~