My 2¢, as long as you are moving forward, you're doing OK. Also there's always someone faster than you.
If you want to be stronger and ride faster... ride more.
Now if you really need anonymous people on the interwebs to make you feel good, then you have bigger problems.
BTW, 20 miles in 1:20 is 15mph. That's a "B" rider and faster than many people I know.