Sri Gour Purnima is the same day as Holi, a festival where mad revelers throw permanently staining DYE at everyone. This day is therefore not a particularly good day to travel. In Barddhaman (Burdwan) the festival of Holi is celebrated one day later.
There is a computerised booking office at Nabadwip Railway Station. It is open 8:00 AM to noon, and 12:30 to 2:00 PM. except Sundays. Tourist quota tickets are only available in Kolkata and New Delhi.