Hi everyone! Yesterday at the ultrasound they said the placenta is low…

Hi everyone! Yesterday at the ultrasound they said the placenta is low, it even covers the cervix... I've been worrying for two days... They told me not to lift heavy things and not to be too "active"... so that it will move up, and the next ultrasound isn't until 21 weeks... girls, who had this? How quickly did it move up?