Whether or not you have to repeat high school freshman year if you are 1 credit short depends on your school district's promotion policies. Some school districts require students to earn a minimum number of credits to advance to the next grade level, while others may allow students to progress with deficiencies if they meet certain other criteria.
If you are unsure of your school district's promotion policies, you should speak to your academic advisor or counselor. They will be able to provide you with information on the specific requirements and help you determine if you need to repeat high school freshman year.