I am sorry to hear about your sexual assault. This has happened to me several times and nothing makes it right.
If the finger had pre-cum or cum fluids, then you should get tested. Semen and pre-cum carry half as much virus as the blood.
Most people would go for the rapid test and then proceed to doubt their results.
My recommendation is that you seek counseling and also, wait three months from the supposed point of infection and get a blood. Wait another three months and repeat the test. Then you will know for sure. If you want to take a rapid test in between, then go right ahead but keep your three months appointments.
In your case, it is not a matter of whether one has heard of cases like yours, the matter is that pre-cum and semen were present.
All the best and

for coming here to get help.
Always
Muthoni (Mson)