Help! I made a knitted DIY scrunchie on a round loom and a hair tie, but it has lost some of its elasticity!?

When I make a knitted DIY scrunchie on a round loom, I bind my project off, and I sew the ends together. However, I can only wrap it around my ponytail twice, whereas when my hair tie is plain, it can go around three times! What am I doing wrong?
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