Of course Golshi would pronounce 고 as 구.

Here it's a way of saying "...I say!" "...so I said!" "...so I told you", "...mm'y'know?", basically affirming what you just said or in this case something you just did or experienced. Pronouncing 고 as 구 in the Seoul dialect is considered cutesy by the younger generation but is also considered annoying by some people. Especially when the pronunciation is dragged out like Golshi does here.