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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The sufficient manner for bowing in the prayer is to bend your body forward so that your hands could touch your knees. It is not necessary to touch your knees with your whole hands; it is sufficient to bend forward in this manner and the bowing is thus valid. Hence, assuming that your finger did not touch your knee while bowing, this does not affect the validity of the prayer.
We advise you to ignore Waswaas (obsessive whispering) completely, as getting carried away with it leads to grave evils.
Allah knows best.