How can I get rid of this crease mark?

Beginning in April, I was on a diet to lose most of my body fat. By June I had noticed some positive results after losing roughly 19 lbs, but during my prom and prom cottage due to unhealthy eating and partying I gained 5 lbs back. To give you an idea I am a 5'7" 18 y/o male weighing around 140 lbs right now, and was 154 when I began. I was in good shape to begin with and now am in even better shape. Part of my reason for beginning this diet was to cut before bulking or in other words lose my fat before gaining muscle in order to just look better for the beach and for my girlfriend and such. However, after that prom cottage weekend a crease mark started being visible just under my top 4 abdominal muscles or half an inch above my belly button. Previously, when I was fatter, this crease mark only appeared when sitting down with bad posture for an extended period of time, but now its here all the time and although I am aware of the fat that it is not really a big deal, it is driving me crazy and I just can't seem to get rid of it! Will losing the weight again get rid of it?

Also, on a side note, i got an ugly tan line right on the patch of skin that the line is on before prom cottage weekend when I sat on a chair and the fat in that area covered the skin so it didn't tan like the rest of my body. So with this hideous line i tried to tan just that area with baby oil and spot treatments and stuff but for some reason it just won't go away. Does this excessive exposure to sun in just that area where both lines are have anything to do with the crease mark? How can I even out my skin ton eon my stomach after this unfortunate tan? How can I get rid of both of them? Please help me! Thank you in advance for any contributors.