LTR 4464C

I submitted my taxes on Feb 4th 2020 , it got rejected because I made a mistake on one of the employment Income verification number , they allowed me to fix it then it was accepted.  My question is , is this why my return was pulled for review or is there something else I should worry about ? I recieved a 4464C letter on Feburary 29th .  And how long does it usually take to receive my return ?