Female, 245 lbs, took 0.25 mg xanax (alprazolam) 8 days ago. have to take pre-employment drug test. am i ok? will it show up?

Probably not: if in fact you only took it once - it is short-acting and its metabolites are essentially gone in 3-5 days. Your weight doesn't really factor into it. However, if you are taking it by prescription, it should not matter unless you are applying for a safety-sensitive position (driver, police, fire etc.). If you are NOT prescribed it, you should NOT be taking it.