Negativity - Negatives Gone Dark

I came back to college a day early so I had time to develop my film before the following day, it was to make sure I wasn't in any rush - I did the typically steps of developing a film, developer, fix and stop - and then wash, it is a long process but worth it when the film comes out and all your photographs are perfectly exposed however after washing my film and unravelling it from the container I noticed how dark each photograph was compared to my last negatives, I didn't understand what went so wrong, I had everything I knew about correct (well thats what I thought) anyways I left my negatives to dry over the night and continue my project the following day.