Mazda BT-50 2017: High fuel consumption

The official fuel consumption (average) is 10L/100km, which is a guide to what you should get, but it will vary depending on the driving conditions, load carried etc. Yours isn't wildly out, and given that it's new and running in you could expect it to improve as it does more kilometres. I would suggest you report your concerns to the dealer and maintain a log on the consumption you get with the view of presenting it to them at the next service. If it hasn't improved by then you should have plenty of evidence to justify your claim that something is not right.