I would like to ask you that do you feel pain while urinating as paun suggests infecction and sometimes can lead to bleeding. As you got the bright red blood it is suggestive of blood coming from lower portion of either urin passage or vaginal passage this may also happen out of minor injuries.
Small amount of blood that to only a single time in urine is not a situation to get panick just wait and watch. If it comes again then you consult a Gynaecologist and get yourself examined and investigated.

Hi and welcome to HCM. The causes of gross and microscopic hematuria are similar and may result from bleeding anywhere along the urinary tract. Infection of the urine, (often called a urinary tract infection or UTI) stemming either from the kidneys or bladder, is a common cause of microscopic hematuria. Other causes are Trauma to any of the urinary tract, hematological disorders, medications such as warfarin. It needs to be diagnosed for proper treatment for which you have to undergo some tests like urine routine, RFT. I suggest you to consult local doctor for the same. It is inappropriate to advice any medicines for you with out proper examination and tests. All the best
Regards
Dr Santosh