I Had a BBL but my Butt is Uneven Due to Long Periods of Sitting and Lying Down.. What Do I Doto Make It Round? (photo)

From your photo seems like the bottom half your buttocks is flatter and has less fat then the top half. I have done corrections previous liposuction and fat injection in the past and corrections have worked well. This requires a repeat liposuction and fat injection into the appropriate areas.

You are very early after liposuction and at this point you can't tell what the final result will look like. It'll probably take you 3 months to get your final look. And you should wait 6 months or more before any further surgery. The longer you wait the less swelling you will have and as your surgeon will be able to get a better result. If you go back to early will be like liposuction in rock but if you go back to late to this result. So you're better off not to rush.

If it has only been 13 days since a Brazilian Butt Lift, you still have a lot of swelling.  I don't see any signs of liposuction though.  Where did the fat come from? 
If it has only been 13 days, your buttocks is going to shrink as the swelling goes away and whatever fat did not survive goes away.  In my experience, most of your swelling will be gone by about 3 months.  That is when you can expect to see what will be pretty darn close to your final results.  There is nothing much you can or should do right now to change your shape.  If you try manipulating your butt, you may damage the remaining fat cells.  Your shape will likely change as things settle due to the effect of gravity.