Do it over and put it back on.==== DETAIL ====The stuff is called anti-seize. It is not lube. Lube just makes it go on easy. Anti-seize is designed to make it come OFF easy. Lube don't last 50K / 5 years. Anti-seize is design to last till you take it off (sometimes 5 years)Modern cars have aluminum heads. They are fairly soft metal. It is possible that you can damage the threading on your heads later when you try to remove the spark plug.====Why it misfires is another question.===Don't forget to vote for the BEST ANSWER - please - whoever it may be.FACT: You also get +3 points when you vote for BEST ANSWER