How to return dates before and after the actual date

Question

Hi my code masters,

Thank you for all the tips you've been sharing with me, it has help my coding development.

please i want to return records of patient three day's before and three day's after the Patient Visit date

i tried using the below SQL statment it's not returning the right records

Select * from PatientVisit where visitdate Between convert(datetime,'"+Textbox1.text+"-3,120) And convert(datetime,'"+Textbox1.text+"+3,120)

any solution will be appreciated.

thank you