OP, not sure how this works now that you are so close to departure, but I've had success getting EC seats on KLM, and having them stick. You have to call DL, and they in turn have to contact someone at a "partner" desk, or something like that. (I've posted details on this in another thread here somewhere.)

The issue is getting an agent who knows what he/she is doing. Again, I'm not sure how this works within the check in window.

Previously, there have been issues on having the EC seats "stick" between the time of securing the seats and departure. I've had success on my last two KLM flights, and on my next DOH-MCT KLM flight, so far the seats are sticking.