interpreting the Scope information
The scope is available after each measure and is lost when you do the next measure, so you do have to look directly after a measure.
It simply gives a picture of the output and input signal.
See a typical measure below where the output is the purple signal from the soundcard and the red is the input signal once it's received by the soundcard. See I have one peak there received that is about 80% of full scale (FS). That's a good sweep signal as long as the meter itself wasn't clipping.
Hard to see anything when you look at the entire horizontal axis of the sweep, so........
Below is an expanded horizontal scale version and you can see the output and input are not clipped. If I increased the input level control so that the VU meter on the Settings page showed more than 0dBFS, then the red signal would be as large as the output signal and you would see the red signal clipping (flat top). If on the other hand, the signal from the meter was clipping, you would see a flat top or other distortion of the input signal without it being 100%FS. This is likely the case when you leave an SPL meter on a lower scale and measure high SPL readings (your case). This is one of the other advantages of a microphone over an SPL meter for measuring audio.