Yes, it's possible to get pregnant this way. If you do this, assume you're trying to get pregnant on purpose. Take a test to be sure.
It sounds like you should learn more about how pregnancy happens and what you can do to try to avoid it. ALWAYS use at least a condom. If an unplanned pregnancy would be a problem for you, then take reasonable steps to reduce the risk... or wait to have sex until you can deal with an unplanned pregnancy.
http://www.plannedparenthood.org/info-for-teens/pregnancy/am-pregnant-33831.asp
You can ask questions here:
http://plannedparenthoodchat.org/