What does releasing the muscle mean? If it is not released, does it cause implant to shift to the right or left? (photo)

Based on your before and after photos I think your results look great. If you are unhappy you should discuss this with your plastic surgeon. At only 6 weeks postop your breasts will continue to change.

During breast augmentation in the submuscular position, it is customary to detach the muscle partially or completely from the rib cage inferiorly while leaving it attached medially to the sternum ( breast bone).  If the inferomedial attachments are left, it can result in lateral displacement of the implant over time, but in some patients with very soft implants( minimal capsule formation), particularly with their dominant hand ( ie for most people right side), the implant will tend to fall laterally when lying down over time, because muscle action tends to push the implant laterally.  Your surgeon used SRATTICE ( acellular dermal matrix) to hold the implant inferolaterally on the right side, and unfortunately, you are somewhat higher, with an irregularity, which may be the edge of the STRATTICE.  You are early enough that with time the implant may drop some, but the matrix tends to hold the position pretty firmly so it may not drop. I would wait 6 months, and then discuss options with your surgeons. Both breasts look nice on your photo, and if the asymmetry improves, and the irregularity goes away ( chances are that it will), I would suggest accepting less than perfect symmetry. 90% of women have some asymmetry visible on photography.

Thanks for the pictures.  You have some asymmetry.  Your right implant because of the SRATTICE will hold its position. To improve symmetry you need SRATTICE in the left breast.  

This is called a dual plane Breast Augmentation.  It allows for expansion of the lower pole of the breast.  The muscle can be released different lengths based on the degree of ptosis. If not released, it does not cause the implant to shift to the right or left.  My recommendation is to continue to massage the right breast as you are 6 weeks post op.  We specialize in revision plastic surgery as seen on Botched.

Thanks for the question, it looks as though you have great results, I think more surgery will expose you to more risk for asymmetry

I see the differences in the left but as compared to your before the result is so much better. I might lipo and try fat transfer in the infer-mrdial left breasts to round it out.