If you have implemented record rollup on Endeca back-end and it is working correctly looking into Endeca JSP reference app. The documentation says passing Nu param and Np param will return aggregated records.But you are not getting correct results from Endeca bridge API.
Simply check bridge API configuration and see if you have added AggRecordsAbstraction. In the config file bridgeproperties_json.xml
<plugin classname="com.endeca.soleng.bridgeframework.plugins.abstraction.AggRecordsAbstractionPlugin" />