As a nurse and a fellow new rider, let me recommend putting ice on that sore bottom when you get home (a bag of frozen peas works great). 20 mins on, 20 mins off, will at least keep the swelling to a minimum and make you more comfortable for tomorrow.

I sat on an icepack myself all last weekend after making the mistake of wearing cotton panties under my bike shorts -don't do it! There's a reason those shorts have no seams down there!