Is it bad on your body to get only 6 or 7 hours of sleep at night?

Sleep. Everyone's sleep requirement is different. 7-8 hours is the consensus 'normal' More concerning is a change in sleep habits or needs.
6-7 hours. Quality 6-7 hours sleep may be adequate as long as there no issues with tiredness during the day.
Depends. Average sleep requirements tend to be 7-7.5 hrs, but this is average and not everyone is the same. 6 hrs seems slow. Your body will tell you if you need more sleep. One indication is if you sleep less on workdays then weekends, then you might be behind on sleep.