If i put my sperm in my gf panty n later if she wears it. .. r there chances of she getting pregnant?

Chance is low: While pregnancy is not likely, the real question should be "how much risk do you accept in becoming pregnant, and are you ready to be pregnant?" if you are not ready, you should modify your activities and use proper birth control and hygiene.

Unlikely: If the sperm is dried on her undergarment when she wears them, then it is unlikely that she will conceive. If the sperm is fresh and still in liquid form there's always a small possibility that it can travel up through the vaginal canal and cause a pregnancy.