The training course went very well in the end. It's just as well we didn't cancel

Hello,
I have a sentence from a test:
The training course went very well in the end. It’s just as well we … (not / cancel) it.

This one is correct according to the answer key:
The training course went very well in the end. It’s just as well we didn’t cancel it.

Is the below sentence also possible? If so, what would be the difference?
The training course went very well in the end. It’s just as well we hadn’t cancelled it.

The training course does not seem to have started well. By and by, it has caught up and improved. So they didn’t have to cancel it as they, perhaps, thought in the beginning. Otherwise there was a possibility of cancellation.

It is possible without the highlighted phrase. That would then mean: We hardly had any hope of the training course going well in the given scenario. We even thought of cancelling it. Now it has proved otherwise (to have gone very well). Thank God, we hadn’t cancelled it!

(This is how I look at the situation)