Oh my goodness, I'm so sorry I missed this tag! Did your gosling finish absorbing the yolk sac and intestines?
Given time they can reabsorb most if not all of the yolk sac. The fact that you were seeing intestines as well is never a good sign unfortunately. A chick/gosling can recover even when the navel closes and part of the yolk sac is still exposed and it will heal, looking much like a black button but that's not the case when the intestines are also outside the body. There would be zero chance of survival if the gosling did not finish absorbing the intestines.
If the gosling is ok, then the most important thing when dealing with navels that aren't properly closed is to keep the brooder area as clean as possible. I know this is much harder with waterfowl but the cleaner you can keep it the better. I also would not allow the gosling to swim until the the navel has completely healed. Applying clorhexidine or antibiotic ointment WITHOUT pain reliever to the navel area daily is a good practice to help prevent infection.
I hope your gosling is doing ok.