If i have plantar fasciitis, it's bad to take 2.5 grams of creatine?

Short-answer no: Plantar fasciits or technically fasciosis is inflammation of the bottom of your foot. Treatment is generally NSAIDs and stretching. Creatine will not have an impact on this.

Will not help: no evidence that Creatine helps with plantar fasciitis. In March 2015, a study published by the British Journal of Cancer found that men using supplements containing creatine may have a higher risk of getting testicular cancer

Not bad, but...: ...not effective treatment. Creatine will not worsen symptoms.