Nexplanon

Teresa
  So I got the implant on 08/03/16 and it was on my 4th day that I started my period. I had sex on the 5th day that I got the implant. My partner used a condom and did a withdrawal on second time. 
   Based on some research I did, it said that if you got nexplanon on your first 5 days of your period, then it will work immediate. If you got it at some other point of your menstrual cycle, then you must use protection( condoms) for a week. Is this true or false? Should I be worried? And how do you know if the withdrawal was a fail ?