The current clamp doesn't have a 1M ohm input; rather, it's output is calibrated to expect a 1M input on the measuring device. So your scope input impedance should be 1M ohm. If it is 50 ohms, you may be burdening the output of the meter excessively, and all bets are off. In other words, it might not just be calibrated into a 1M ohm load, it might be incapable of driving a lower-impedance load. The readings would be lower than expected.
The other related error is a device that produces an output expecting to go into 50 ohms. Here's the thing: if you have an output impedance of 50 ohms, and an input of 50 ohms, and you connect them together, you have a voltage divider. The output produced by the (whatever) is living half within output impedance of itself, and half within the output of the receiving device. So the output that's produced is twice what you expect the reading to be, because you're only reading half of it.
On the other hand, a device that expects to see a 1M ohm input impedance will typically have a very low output impedance, relatively speaking. So we have, more or less, a nearly-zero output impedance connected to a nearly-infinite input impedance. This, again, forms a voltage divider, and almost all the output voltage the instrument is producing will live in the input of the measuring device. In such a case, the output of the producer should expect to produce the voltage that should actually be read, since none of it's getting lost in its own output impedance.
You are measuring three lines; each appears to be at about 280mV peak or so, which means each one is carrying about 7 amps peak, assuming peak is what you want to know. I have a suspicion it should really be RMS, and that puts it at about 5 amps each, but I do not know.
And then I also suspect there is something you'll have to do with combining the three legs. They are 120 degrees out of phase with each other, and so they are not simply adding up; there are vectors involved. But they might be adding up if you're using RMS values... these are things I do not know. If I were in your position, I'd start studying three phase power and how to measure it. There seems to be some references on the interweb; poke around a little and see if any of them help you understand what's going on. They speak of the sqrt(3) / 2 and that sort of thing. I would guess it applies here somehow. Maybe.