This seems to be worrying more people, because of the reverse applique. I tacked/basted my pink behind the black, either side of the line, leaving a little room to tuck the black under.
Then you have to cut the black down the middle between the two lines. If your block is enlarged, you have enough to tuck under. If you are working with a 7in block, you might consider making the two lines just a little further apart if you are worried that you won't have enough to turn under. Either way, don't cut down the middle all the way round, just an inch or two at a time, and I had two needles on the go, so I could stitch along both sides before I cut the next section.
Details, showing basted lines, cutting down the middle (only cut a little at a time), Turning under and sewing down
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I've done a bit more in this pic.
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The back, with the pink cut away - this way, you can use what is left over in another block.
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Detail
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The 'ring' finished on the front
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The 'underneath' leaves added - no need to tuck under where another leaf is going on top. Note I have redrawn the liines on top of these leaves, so I will be able to follow them when sewing on the next lot. Sometimes an ordinary (grey) lead is easier to see.
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Next layer added. (I am still cutting away behind, as I go.)
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Finished
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The back
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Detail
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