My vote is to keep the fish, and make sure you stay constant on your water changes. If you keep the water quality up, then eventually it will get to the point where you will see that the fish have a hard time moving around because of their size. At this point you can show them to you mom and say something like "I have been taking great care of these fish for the last year, and now even though I keep their water as fresh as I possibly can, they will die soon because it is hard for them to even turn around in this small of a tank. Do you think I could give them away and find a fish that will stay small to replace them?" Most kids don't have the responsiblity needed to care for fish over the long term, so I am sure that your mother will soften up to the idea once she sees that you do have the responsibility needed. In a years time a lot can happen and you may end up with a bigger better setup. Who knows!