What matters is that you've still reduced suffering and your own environmental impact by going pescetarian/vegan.
Just try to be more forceful next time and fully explain your reasons for becoming vegan. It can be hard without family support, though, although I tend to find the dairy products are the hardest to cut out. Is it just fish that your Dad tries to feed you or other animal products as well? You could stay a pescetarian until you live by yourself, but even then, remember that no one's perfect - vegans have an impact on animals and the environment too, just less so than omnivores. It's a continuum, not a do all/do nothing dichotomy!