It definitely is not Mimosa pudica. However, Albizia julibrissin comes closer.
Here is a full grown AJ:
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Perhaps it is a baby AJ?
Desmanthus spp. comes even closer, although has smaller ridges surrounding each leave, unlike the leaves on your plant which are smooth and flat from what I can tell. If I were to guess, I'd say a type of Desmanthus.
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Another type of Desmanthus known as Desmanthus pernambucanus looks similar, perhaps wait for the flower to rise and that should give you a definite answer.
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Hope this helps!
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