Found of a site.
How long sperm can live in the open-air depends on the situation, what kind of environment it's in and how much sperm is present. But, on average, sperm can't live for much longer than a few hours in the open-air. It's important to remember that if sperm is inside a women's body, it can survive for up to seven days.
There is a risk of pregnancy if sperm comes into contact with the vagina in any way including from sperm on fingers. If you think that sperm may have come into contact with your vagina within the last five days, and you don't want to get pregnant, you should seek advice on emergency contraception as soon as possible.
If you think you might be pregnant, for example, if your period is late, you can get a urine test done to find out for sure. Most pregnancy tests state that they work as soon as a period is late. If you don't have a regular cycle it can be difficult to know when your period is due, so it's best to take the test three weeks after having unprotected sex (as this is roughly how long it will take for the hormone levels to show up on the test).
But the chances of The girl getting pregnant from a small dose of c** from a finger that 'may' have been there is a little far fetched.