Unfortunately, the blood found on your finger did render you niddah. It is comparable to a bedikah in which even a small amount of blood is problematic (even less than a gris).
You should wait five days before performing a hefsek taharah and starting the seven clean days.
For the future, if you find a questionable stain on toilet paper (after waiting between urinating and wiping) you can wipe again to check if there is any more staining but you should not check internally.
Please feel free to get back to us with any further questions.
B’hatzlacha!