THE CONDOM BROKE! PLEASE HELP!

Br
my boyfriend and I have been together for a while but we are still young , 17 & 16, no biggy both of our parents know we are sexually active! 
We've been having sex for a few weeks now and we'll today we had our first accident! We were having protected sex (meaning he was wearing a condom) unfortunately the condom broke and we didn't know until after the fact of him ejaculating inside me. We instantly went to the pharmacy to get Plan B. I'm just really paranoid because I don't get my period regularly and this is my first time having a to take plan b.
Has anyone else been in this situation? 
How'd it work for you? 
Any thoughts, please anyone who can help calm my nerves!