My essex retainer is cracked, is it still usable?

So, I've been wearing my retainers since may of this year, when I got my braces off, but the top one cracked at the very end on both sides, at the molars. I can still feel the usual pressure on my front teeth, but on the cracked parts it splits when I put it in. Do I have to replace it, or will my dentist fix it? Will I have to pay for it? I don't know if it broke because I put it in wrong, but it did.

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