HIV cannot infect outside the body. Any sperm that landed on you was exposed to air and therefore lost the ability to infect. In an adult, the only way you can be infected is through unprotected anal or vaginal sex or by sharing IV drug needles with infected users. What you've described is not a risk.
I am not quite sure I know what you mean. Are you saying that this man ejaculated on your legs or near/in your vagina? If it was on your legs you have absolutely nothing to worry about. However, if it was near/in your vagina you will definitely need to check it out. An HIV test is a very simple blood test and takes a couple of days for the results to come through. You would then need to follow up with a doctor. If you do not know if you had a cut or blood (?) it would be a good idea to check it out.