Ultrasonic Sensor Controller
Ok, let's remind ourselves how ultrasonic sensors typically work:


Send out a pulse
Wait for echo


Looking at the datasheet, after your initial pull low, the output goes high, then goes low whenever it detects echos. The examples given in the datasheet are for perfect (maybe even simulated) conditions.

So, what I see from your scope looks correct! After your initial pull low, the sensor sees an immediate echo (from itself) which it is designed to attenuate (ignore) - that's that tiny blip. Then the output goes high (waiting for an echo). Then it starts getting echos - apparently a lot of them.

So, what you need to do is pull it low, wait until the signal goes high, then start timing how long it takes to go low again (first echo). If you care about other reflections and multipath, you may try to analyze the remaining.

But dude, it's working fine!