I am wondering if anyone else has had this problem.  I had a RFF and the phallus is a bit "flabby" like it doesn't have enough filling. My surgeon recommended fat grafting which I did but most of it didn't take and I'm in basically the same situation. I'm concerned about how it will work for penetrative sex. Wondering if there is anything else I can do before getting my erectile implant or what results others have had.

This is fairly common. I think most people find that the erectile implant fills everything out to their satisfaction. The longer term for fat grafting is *serial* fat grafting, meaning it is usually done over multiple sessions because not all the grafted fat will survive. You could speak with your surgeon about doing more fat grafting before getting the implant, or hope the implant provides more of the volume you'd like. Fat grafting after getting the implant wouldn't be recommended due to risk of infection.