All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
You should avoid Waswasah and not pay any attention to it. Just touching the pot with which you performed Istinjaa’ does not render it impure, and you should not rule that something is impure just by doubt, as in principle all things are pure.
Also, if the water that has impurity is separated from the impurity without being changed by it, then, according to many scholars, it is ruled to be pure . Please refer to fatwa 321763.
Hence, if we presume that what you said is correct, that the water that fell on your finger that is impure then separated from it without being changed with the impurity, then it is ruled to be pure.
In any case, you must ignore such Waswasah and not get carried away with it, as letting yourself get carried away with it leads to a great evil.
Allah knows best.