Average Stars in my Backyard

So I did a night time observation right in my own backyard.   I took a toilet paper roll and counted the numbers I saw through it 20 times.  So the total number of stars I saw at 9:30 p.m. on June 24th was 19.  Divide that by 20 and I got 0.95.  It was pretty low, but that was expected for my area because I live right behind an elementary school.  The new lights on the building aren't as bright as the old lights, but it still gives off a lot of light.  When I multiply 1.9 by 99.3, I can see a total of 189 stars in the sky (rounded).  It's not a whole lot so it shows that there is a lot of light pollution around my home.