Generally speaking consulates from Schengen countries can issue what they deemed appropriate, you can't apply for a “90 days visa” or a “30 days visa” or anything like that. So if you submitted an itinerary for a business trip with meetings spread over ten days, you might receive a visa covering only that and you can't expect to get some sort of standard visa that would allow a longer stay.
If you did however submit a longer itinerary with all the necessary documentation, it's also possible they simply made a mistake. You can always try to ask them to reconsider (informally, as there is a procedure to complain about refusals but nothing if you did get a visa).
In any case, you can't generally extend a short-stay visa from within Spain (there are some exceptions but they won't apply to your situation).