Although mine is a radical outlook, I think the simple reason that you have so much of a Pisces influence is simply because, at the time of your first breath, Pisces "took" (in your field) more deeply than did Cancer; maybe this had to do with pre-natal "settings" making a Pisces susceptibility greater, maybe to karmic trends, who knows?
In any case, I have come to believe that signs-and planets-"take" or "hardly take" at birth, due to a pre-existant susceptibility of the individual (please note that this idea is hardly known in either Western or Vedic astrology, although a similar concept-that of the natal swara-is current among many of the Jaimini vedic adepts)
There is an alternative explanation (to my radical one) which the old time Greco-Roman astrologers (like Marcus Manilius) would have given to explain the phenomena:
-by whole sign (the only house system they knew of) Pisces is in the 10th house (I'm going by memory here because the chart is no longer displayed); the 10th was considered the second most potent pivot (angle) in the horoscope by the old time Greco-Roman astrologers
-according to them (Manilius) Pisces is a nocturnal sign, and this is a nocturnal (night) nativity
-so, Pisces is doubly strong (because of being in the 10th house and because the nativity was at night)
-(as I remember) the sun sign Cancer is in the 2nd house (by whole sign)
-the 2nd house is a succedent house, the 2nd house considered by the old time Greco-Roman astrologers as being the 6th most potent place (house) in the circle of the 12 "temples"
-Manilius says Cancer is a daytime (diurnal) sign
-so Cancer is only at the 6th most potent place (compared to Pisces at the 2nd most potent place) and Cancer's influence is further modified by its being a diurnal sign in a nocturnal chart (Pisces is a nocturnal sign in a nocturnal chart)
The old time Greco-Roman astrologers would easily understand why Pisces had the greater influence over Cancer in this nativity.