Hi and welcome to the site. 🙂
Vauxhall/Opel list in the Owners Manual that acceptable oil consumption is 1 Litre per 1000 Km (600 Miles) so it would appear you are within that but just ensure it doesn't go below the 'Min' mark on the dipstick as these engines (like most) don't like running on a low oil level.
My Vectra B SRi has had the GM fully synthetic 5W30 from new and at 120,000 miles only consumes a small amount of oil. Let the engine warm up fully before accelerating hard.