Why would you need to pee where there is no restroom? Can't you leave, and pee some where else? Or not go to this place?
Do you need help?
Do not pee through the panties. Aside from being embarrassing, wet urine soaked clothing can cause skin irritation. Babies get diaper rash if their diapers are not changed. This is from the urine soaked diaper being against the skin. If left for a long time further infections can happen. For example urinary tract infections or bladder infections. This same thing can happen to a grown person if they pee themselves, and do not change clothes.
Diaper rash or rash from prolonged skin exposure to urine can cause the skin to turn red, itch, sting, or even feel a warm burning sensation. It hurts.
At the very least pull the crotch of the panties to the side to pee. Do not pee through the fabric and continue to wear it afterwards.
Please use the internet to get help if someone is forcing you to be in this situation or is hurting you.