Well shrinking penis might be highly subjective. Or did you measured size differences in your fully erected penis (I mean rock hard, which not many of us have pre-boot)? Flaccid penis size is highly variable. During reboot I have days when my dick looks small but I have days when it is bigger than usual but it also was happening pre-boot (you just have not been noticing it). So i would not worry about that at all unless it shrinks inside of your body