Yes it is very normal if you play with it a lot, tongue rings will stretch no matter what because when you eat a lot of people tend to bite it, I bite mine all the time when I am eating.
But that only stretches it a little, if you constantly play with your tongue ring, like I do you will stretch the hole, but it's not noticeable.
If you were to actually try and gage your tongue piercing then it'd be noticeable, but if you're not gaging it and only playing with it, expect it to stretch, nothing bad will happen.
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