Well done, a long way for a first ride. Mine was 7 miles and I thought I was going to die,Went on my first ride today did about 15 miles.
And please do not purchase a saddle cover; riding little and often will allow you to adapt to cycling including getting your arse used to sitting on next to nothing for hours on end

As above you may need a different saddle (I use what came as standard on my road bike and use a Charge Spoon on my hybrid).