Ok, I will do this in the future.
I had got the impression, from videos I had watched and forum posts I had read that you should just wait for a contact me message. Also, earlier in the flight, I looked on VATSpy and it said I was in London Center's airspace. So I checked in with london center and he said "you're not in my airspace, monitor unicom 122.8". So if I'm not sure, I should always contact them?
Thanks