Can your agent change your premium price after you paid the premium in full I paid for a 6 month policy IN FULL and the 45 days later my agent said I owe 192 more due to HER mistake Is it LEGAL?

In most US states an Insurance Company has 60 days from policy inception to properly adjust a premium. Most often a premium change is the result of some unknown factor at policy inception, Usually undisclosed tickets or accidents on the part of the drivers on the policy.