Is there sopose to have a not under my chin ?

No: If it enlarges or does not go away in a few days, would get it checked out.

No, thats unusual: It could be an enlarged lymph node, a cyst, or a benign or even malignant growth. The most common cysts would be thyroglossal duct cysts, sebaceous cysts, salivary gland cysts and dermoids. Without knowing more it's impossible to say. Get examined by an ENT who may recommend a needle biopsy and imaging with ct or ultrasound.