OnRamps HISTORY decline or accept?

Hello! UT is a dream school of mine but right now I have a 78 in my OnRamps history course, I told my HS teacher I would decline the credit but he said that I should just accept it because UT will let me retake the grade in college and the 78 will go away. Is this true? Also I want to be a dentist and get a bachelors in something of that degree, will I need History for my bachelors, and will it drop my GPA? Thanks!!