Why did I get a bag after tear trough filler with micro cannula? (Photo)

I dont see enough excess fat to warrant eyelid surgery. There is very little margin for error when injecting the under eye area. My personal opinion is that I get much better results when using needles compared to using a microcannula. A microcannula needs to be inserted under the skin through a single puncture wound and then guided to different positions in the eyelid. In my experience it is very difficult to get the cannula to the right place and right depth throughout the lower eyelid through this single entry site.I suspect other doctors will have different opinions on this topic. My recommendation is to find a doctor who has a lot of experience treating the under eye area and then go with whatever method he or she recommends. 

Difficult to say from the pictures.  The lighting is different and left and right look different.
Cannula is generally seen as safer as less likely to inject into a blood vessel.  But this does depend on the injector.
You seem a bit young to have eyelid surgery.  
I would suggest seeing your injector again and discus your concerns and come up with a plan.
Time is also a good predictor, don't rush to have more filler and other treatments.

This may be due to injector technique, but keep in mind a combination approach is needed to get improvement under the eyes. Fillers, lasers, and microneedling/PRP can improve under the eyes. My patients try to get non surgical treatments to avoid surgery. We use PRP and stem cells there often. I suggest consulting with an expert to develop a treatment plan best suited for your short and long term goals. Best, Dr. Emer