That's annoying Ron. I clamped the template to it for guidance so all holes lined up - I will have to check the bed on my pillar drill as it can tilt for angles perhaps that was why...
It is a bit fragile when thin due to it's hardness I have found - the drills clog and heat is a problem - I learned to up and down a lot and stop and unclog but it was still a problem.
Heat / expansion probably caused the crack - I did not see it. Will drill even slower next time.
Ideally you would use some washers under the mounting bolts as they are M4 and the holes are as the template M5.
Also I would guess your blind nuts are the same as Martin's and they are aluminium rivnuts - do not over tighten as the ali is not very strong.