[Arctic]

David.
Top up the tank to the required level run the car then look under to see if the bottom hose as sprung a leak, also check the Y section where the hose was fitted as these can be brittle and leak after fitting an inline stat, when you have fitted a inline stat it is always best to give the car a run so the stat can open up properly.

This should have been done before leaving the Nano, by yourself or with someone with you then returned to Nano for car to be left on tick over for at least 20 minutes.

I doubt you have done any damage to the car but the leak needs to be found asap, do not drive it until you have.