You were expecting what?
You have a high output for 500uS, then a low for 500uS, then low for ~110uS while the analogRead of the low output happens, then low some more while the float math happens, then low some more while Serial.print runs, and finally low some more while loop completes and jumps back for the digitalWrite to finally go high again.
analogRead returns a reading of the decaying capacitor multiplied by 4.88mV, so you might get something other than 0.
Plug in your RC values here here and get some idea of the responsiveness of the output:
http://sim.okawa-denshi.jp/en/CRtool.php