Should I be concerned with the gaps in my donor area 16 days post FUE surgery?

4800 FUE graft at once is considered a very high number of graft surgery and as such you will expect gaps in the donor area.  It will take several months to see what it may look like but if you keep it as short as you do in the photo, the gaps will likely still show since the hairs will be missing.4800 FUE "GAP" made with a 1mm diameter tool is a GAP equivalent to 38 square centimeters.  This empty GAP is about 3/4 the size of a Post It Note.  This empty GAP is about 5 SD (Secure Digital memory cards) put together.

At 16 days, the hair in the transplanted grafts will have started their natural post-op shedding, so gaps in the recipient area are natural. There should not be gaps in the donor area if the area was harvested evenly. However, it is very difficult to tell the final appearance at 16 days. It is also possible that there may have been some donor shedding (effluvium) after the procedure that will reverse over time. 

While 4800 is a very large quantity of grafts it is difficult to determine if they over harvested your donor area or not yet. If not due to shock loss and if they took the appropriate amount of grafts from your donor area then your skin / donor area should retrieve it's original density within a few weeks / months.At this point just be patient and see if you retrieve that normal appearance.

Although 4800 is a lot of grafts to obtain by FUE on a second procedure, It's too early to say how the donor area will settle out- give it a few months before you start to worry.

Sometimes  there may be such a early phase alopecic, bald spots  in donor areas after FUE surgery,  but fortunatelly most are transient. İt may happen because of over harvesting or transient post traumatic shedding /shock loss. Any way it heals and hair regrow in 4-5 months of hair restoration surgery .

It is not unusual that that gaps may appear as the grafts shed after the original surgeon. Never judge the results at 3 weeks.