I came inside a girl but she said she not pregnant. is that true

Hard to say: If you are having unprotected sex, pregnancy can result. If it has been a couple months and she is still having her menstrual cycle, this may be true. If this has been recent, only time will tell. If you don't want to be a daddy now, take care of the issue yourself and use condoms.

More info needed: Can't answer this with limited info. Was she on the pill? When was her last period? Where is she in her cycle? If she does not get menses at the expected time she should take a test. She should also see a clinician to obtain birth control. Condoms are a good idea also.