You can get pregnant if ejaculate comes into contact with your vagina, whether inside or outside. The risk is obviously greater if he ejaculated inside of you. But there's still a risk anytime you mess around and get sperm near your vagina.
I think you're fine =)
Yes, sperm can travel up the vagina but, it has to have a medium (fluid) to swim in, i.e your vaginal fluids. It cant "crawl" from the outside of your skin and into your vagina. Now, if he is ejaculating near the opening,or the sperm "dripping" to the opening, there may be a greater risk.
If you're not ready to be pregnant, practice safe sex. Not only to avoid getting pregnant, but also to avoid STD's. BTW, if you have a normal 28 day cycle, you ovulate 14 days after the first day of your last period. That's not ALWAYS the case with every woman, so don't use that method to avoid pregnacy. Be safe all the time, everytime.
Relax!!!=) You're fine. If you need the piece of mind, take a pregnancy test***