It's not your fault you were given bad advice. Goldfish are supposed to keep growing and growing and live a really long time, not die after a few years like so many people assume. If they stop growing, it means something's wrong. Your goldfish will be fine in the pond as long as they're big enough that they won't fit in the koi's mouths. If they're not big enough yet, and you start changing a lot of water, ideally every day, they might start growing again so you can eventually move them to the pond. I'm not sure. Someone with more knowledge of goldfish can chime in.
They only grow to the size of the tank because their outsides stop but their insides do not.
Hi Bowens, it's great that your so excited, but if you can find a local pond at a park or somewhere, the fish would really appreciate it, I took my grandsons to our local pond, and we go every month to feed them, they can stand the cold as they are not tropical, then you could get some smaller tropical fish, you would love, just ask some questions on here first before you decide.........