im not really sure whether the sperm splattered on her panties, but high chances are not. i went and wash my hands and washed her hands. she should be fine right? im worried that a small amount actually reaches the vagina
It's natural to be worried but from the way you described it, the chances are just about 0%. Even if semen reached her panties it would have to enter well inside of her, which is not likely to happen all by itself.