Code looks complete to me. No need to use a library for this simple sensor (but adding a timeout value to pulseIn() is a good idea).
The delay(50) plus time taken for the Serial.print() calls should be enough for echoes to die out.
Wiring firm? No loose contacts?
And credit for managing to get an image in your post, but it's much better if text output is given as text rather than as image of such text (use code tags to preserve formatting if needed).