Can you swim on your period?

I got my period for the second time today. The problem is I have a swim meet tonight at 5. And no I can't skip it I already said I was coming. I texted my mom but she is at work until 7 so cannot help me put in a tampon. I am to scared to anyway ad he knows that because she tried to help me the first time. It is not very heavy and did not leak through my pants and is not on my leg at all. I was wondering if I could swim with it with no tampon. I will only be in the water for about 40 sec then get out. I have a swimsuit with black lining. Do you think it would be ok for me to go swimming with my period?