It should be okay, as people have said, tell your doctor.
wearing a tampon may help as long as you hold the string out of your urine stream.
I was on the end of my period once when I got a urine test and she did actually have to ditch it as it was a protein test and the blood screwed it up.
She gave me a cup to take home but only to use it if I didn't get better.
I hope your test goes okay