if you are not alloted in third allotments then you must try for real time allotments by being present there
the date for the real time allotments are there on the official site of cusat under schedule for btech councelling you should be present accordingly
whether it be for the verification of documents for the first three allotments or the real time councelling in any case you have to be present there so get your tickets booked and attemd the real time allotments
best of luck