morethan1 - from the crack pattern, it looks like the object was lifted while still being strongly adhered to the glass.
What did you use on the glass? Glue stick or something else? Did you use a very thin layer?
Did you wait for the bed to cool completely?
When I got my previous printer, I'd try pry off the object before cooling down, and some of them would just not let go.
But I quickly learned that patience pays off. Just wait a couple more minutes, and you should hear the satisfying pop as the object dislocates itself.
Also, you can try a mirror. I've used mirrors from IKEA before, and they work fine. (Unless you're printer below mm layer height)
if it isn't broken, you haven't modded it enough