Just took a tubal ligation class and part of it was explaining the failure rate and why. If you didn't just have a baby and had it done, the probability is you were already pregnant when it was done. Looking at the day you had it done to todays date, I would say that you were already pregnant and it more than likely isn't an ectopic pregnancy. Hope this helps.
Also, was it done by chance during a c-section?
Im not to sure but I would definitly have a sono done to make sure. These things happen. Did you just have a baby?
Do you know what form of ligation you had done?