Is it ok to go the dentist when your lip piercing is not fully healed?

It isn't harmful to your piercing, your dentist will usually work around it, although some don't like to. Most places are pretty good, I'd recommend you call your dental office and explain that you have a lip piercing you have gotten recently, at worst they will suggest to reschedule your appointment. Although be prepared for a lecture from your dentist on how harmful lip piercings are to your teeth and gums. Trust me on this, I've had it happen twice. Lol.