Analyzing double bubble issue
The picture does appear to show a double bubble. It can be caused by either the pocket extending below the original fold, or by the pectoral muscle pulling up. If you see the crease pulling up when you flex your pec, then that is the cause. It can be corrected by converting to the split muscle plane (NOT dual-plane). If it does not pull up, then it is the pocket. It could possibly be improved by tightening up the bottom part of the lift, assuming you like the position of the implant.
Breast augmentation with Sientra Implants
This picture shows the lower inner pole of the right breast but I cannot see the other areas. If you have a pre and post that will help. Contact your surgeon if this is an abrupt change when compared to the other side.
You are still very early in the healing process. Lifting your arms may distort things at this point. From the photo, it does seem like you have the beginnings of a double bubble. No corrective surgery would be indicated now. You need to wait and let things heal and may find that you end up with a very nice result and without a double bubble.