Neon Mascara Tank JR Athletic Work Out Medium

I have not seen this sizing before but my research says it is a Jr. 2x/3x. Looks like it would be equivalent to an adult Medium, but Check these measurements. It has stretch, 10% spandex. Contition: no stains. No holes, unworn. One of the bright seams looks uneven, see photo. Smoke-free, Pet-Friendly home. Measurements laying flat: underarms 16.5, length 25" from shoulder down, bottom hem 17.5".