I Was Given Clindamycin 300mg Hcl For An Infected Tooth

I was given clindamycin 300mg Hcl for an infected tooth by my dentist. After he attempted to repair a filling I began to have severe pain about two weeks later. He says I need root canal. My concern is that he set my clindamycin dose at twice a day when everything I've read seems to indicate that's not enough. Most doses are there to four times a day. I can not take penicillin (anaphylactic) so I am concerned about creating resistance and the infection not being treated properly. Is 300mg twice a day ok?