I'm 3.5 months post op. By looking at my picture, am I going to get good density after 6/7 months? (Photo)

No way to tell what was done or how may grafts were transplanted with a single photo.  Results of a hair transplant surgery is generally related to the number of grafts that was transplanted, where it was transplanted, and the skill set of the doctor who did the surgery.  

At 3.5 months it is not possible to predict! Some individuals do not have any growth at 3.5 months. Results take about 1 year. Density comes from two factors- how many grafts are put in AND how many end up surviving.  The survival rate is dependent on many factors including how the procedure was performed. 

I always tell my patients not to look at their hair transplant for 7 months, when reasonable growth it present. If you look at the area at 5 months, although some of the grafts will have grown, you will only be disappointed as the rest may not have started to grow for another month or two