you either ordered or got the wrong exhaust system.
If the 2 Bolt Flange is free floating you can cut it off and get a retro fit unit from most aftermarket parts places.
If it is welded on you'll have to take the pipes with the two bolt flanges into a muffler shop and have them weld on the three bolt flanges (should be around $50 for the two of them)
TYPE-SSQV 2.5" ALUMINUM TURBO BLOW OFF VALVE FLANGE PIPE/PIPPING ADAPTOR SILVER, US-Car TYPE-S CARBON TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MAZDA TYPE-S CARBON TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, AUDI VW TYPE-S CARBON TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, US-Car TYPE-S BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MAZDA TYPE-S BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, AUDI VW TYPE-S BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, BMW MINI TYPE-S BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, AUDI VW TYPE-S RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, US-Car TYPE-S RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MAZDA TYPE-S RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, BMW MINI TYPE-S RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, AUDI VW TYPE-RS GM TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, US-Car TYPE-RS GM TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MAZDA TYPE-RS GM TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, BMW MINI TYPE-RS GM TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, US-Car TYPE-RS BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MAZDA TYPE-RS BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, BMW MINI TYPE-RS BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, AUDI VW TYPE-RS BLUE TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MAZDA TYPE-RS RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, BMW MINI TYPE-RS RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, MIT EAGLE TYPE-RS RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, AUDI VW TYPE-RS RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, US-Car TYPE-RS RED TURBO BLOW OFF VALVE BOV+2.5" FLANGE ADAPTER ALUMINUM PIPE, BLACK TURBO BOV JDM RS STYLE FLANGE SILICONE REINFORCED ADAPTER PIPE 2.5" SUBARU, BLACK TURBO BOV JDM RS STYLE FLANGE SILICONE REINFORCED ADAPTER PIPE 2.5" TOYOTA, BLACK TURBO BOV JDM RS STYLE FLANGE SILICONE REINFORCED ADAPTER PIPE 2.5" NISSAN, BLACK TURBO BOV JDM RS STYLE FLANGE SILICONE REINFORCED ADAPTER PIPE 2.5" MAZDA, BLACK TURBO BOV JDM RS STYLE FLANGE SILICONE REINFORCED ADAPTER PIPE 2.5" HONDA,