I wouldn't worry at all about this level of radiation. To quote from the Health Physics Society position statement on radiation:
"There is substantial and convincing scientific evidence for health risks following high-dose
exposures. However, below 0.05–0.10 sV (which includes occupational and environmental
exposures), risks of health effects are either too small to be observed or are nonexistent."
The measured dosage you listed is 0.00027 sieverts.
Don't forget that the existing regulations which limit exposure aren't the levels at which the danger starts. They are the values where danger starts divided by some very very large fudge factor! In your case, the Netherlands government chose a fudge factor (safety factor) of 50x.