How not to assemble a 5 foot long tongue and groove joint

I am building a camp trailer. The floor is 5' Wide and 8' long. I cut an awesome dry fit tongue and groove joint. I am not a woodworking. I ended up using 200# of weight and an 8# sledgehammer to assemble this joint. In the end the joint is flush. The long sides are even. The short side is 1/4" short. Miss matched. I will have to trim this mismatch tomorrow after the glue sets. If you what I did wrong please post in the comments. My current theory is that 1) the glue caused the wood to slightly swell and 2) the glue started to set because it took me to long to get the joint together. I don't know what happen. It will work out but after 20 plus minutes swinging the sledgehammer I was whooped