I've started reading in a WaveFlow without first fixing the pulse constant. I've also not entered the correct Start Reading from the meter.
The result is that my totals in Plug and Play Scada are all wrong. How do I get rid of them? It doesn't allow me to delete them in the Edit->MeterTotals screen.

You can enter a manual total over an old meter reading total. Usually it is not a good idea to delete a meter total, because it will just be read from the meter again and inserted wrong, so it is best to recalculate the total based on the fixed profile, and then if there is a total there, the total read from the meter will not be used to replace it.
But in the case of the WaveFlow, you can simply delete the total, since (at the time of writing) it doesn't keep historic totals.
In order to get the delete/recalculate options on such a total, enter a manual reading over it at exactly the same timestamp. The reading at that timestamp will then become editable.
I suggest that you then also do a 're-interpolate all' on especially profile-less meters, e.g. the Wavenis Pulse meters, in order to keep your totals and profile in track. The profile for these kinds of meters are all interpolated in any case. With a profile meter, you would first fix the profile, and then recalculate the totals to fit in with the profile. With these meters, you would first fix the totals, and then do a 're-interpolate all' to fix the profile according to the totals.
If you forget to do the re-interpolate all, or you do not delete all your bad totals, the system will try to reconcile any new totals that you read with the existing profile - which is a bad idea if you've really messed them up. So, if you really did bad, delete all the totals, and delete all the profile (through 're-interpolate all').

One quick way to delete totals is to go to Edit->MeterDetails and set the maxdate back (while checking the checkbox to say to delete totals also).
Once historic profiles are read from the WaveFlow, you might have to enter the wrong historic totals that are still in memory as something like the start reading, so that they don't get overwritten again with nonsense when the meter is read. However, it might be that the reconfiguration of the Waveflow has cleared its memory, in which case you can still just delete them.
Remember, it is important that the historic record of the totals and profile must be correct and internally consistent with each other. That is one of the basis building blocks of Plug and Play Scada as an AMR.