New build, oil in the water

I just got my motor running today. It's a fresh rebuild. It seems to be running great but there is oil in my coolant. Not a ton but enough to make me worried.

If my head gasket got fucked somehow would my car still run just fine? Is a little oil normal after a rebuild? I did not do the build, but the engine did come to me with the head off of it. A professional also put the long block together.

Does anyone have any thoughts on this?