Rfg for 25 gallon peninsula

[CoryEaster23]

I have a 25 gallon wb peninsula and just bought a rfg to see if it would help the flow in my tank. But when I went to snap on the part that threads to my return hose to the rfg, the rfg side was too big. I'll post pics for better clarification. But no clue what I need to order to make this rfg work properly.

 

[blaxsun]

Yes, pictures will help a lot.