Never received amended refund

I received the CP21B letter regarding my amended 2024 return. It states I would receive my refund within two to three weeks from the date of the letter if I hadn't already received it. It is now May 23 and I have not received the refund check. That is 11 days after the time frame given. Should I give it more time or file form 3911 (Taxpayer Statement Regarding Refund)?

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