If the paper was tough, then the same case must be there for everyone. Don't worry for the results. They generally give away the grace marks to let the candidate pass only when he/she is somewhere lying close to the minimum passing marks. And if the question paper was tough then surely there will be some kind of leniency shown by the invigilator while checking the answer sheets.

if all over the question paper is tough then deffinitely you will get grace as well as linient checking will be done but if only one quesion is given then no linint checking will be done in any case they will check linient checking in that particular answer. so all the best.