Hi,
Some of what you are seeing is the scopes performance. The top of the screen says 1G sample per second and 60 points. I assume that there are only 60 samples for the information displayed. The scope is joining the dots between the samples. I don't know if the Rigol scope has an option to highlight the data points or turn off the vectors.
If you turn on a second channel, the sample rate, per channel will drop to 500 Ms/s, and see if this changes your waveform.
This scope picture from my TDS744A converted to a TDS784A has 100 G samples per second, equivalent time, so there is 100 time more information used build the waveform. This requires a repetitive waveform to acquire all the samples.
Regards,
Jay_Diddy_B