Can't retrieve fields in pugin

Hi,

 CRM 13 On premise.

I'm having some problems to retrieve an opportunity's fields. Basically the problem is that the code that retrieves the opportunity always gets the same columns, even if I specify them, here's my code:

Entity Opportunity_Target = (Entity)_service.Retrieve(entity.LogicalName, entity.Id, new ColumnSet(new String[] { "total","statecode" }));

The result of this is Opportunity_Target with 9 columns, any of those were mentioned in the ColumnSet above.

'entity' object is being received as a parameter, and it's an EntityReference pointing to the regarding Opportunity.

What could be the problem here?

Thanks in advance.