you had sex last night?
go now to your nearest plannedparenthood or similar and get the morning after pill.
it needs to be taken within 72 hours of unprotected sex - the sooner the better.
while there discuss future birth control so you don't find yourself in this situation again.
the day your period finishes is totally irrelevant.
the day it starts is the all important day.
if I were to assume you have a regular 28 day cycle and your period began on march 08 then your "likely" ovulation would be around march 22.
sperm can survive for upto 5 days inside the fertile female.
the egg is good for about 36 hours after ovulation.
so your window of likely highest fertility is from 22-5=17 march 17 until march 23/24
now when I say likely that means based on averages and assumptions with an educated guess here and there.
I do not know when you ovulate (release an egg), you could be an early ovulator or a late one.
as you can see you are borderlining the window of high fertility for an average cycle.
really your best option is to go to a plannedparenthood or similar as soon as possible.
once your period is due or late then you can take a test to see if you are pregnant or not.