1: You are not supposed to do a full water change. 20-25% daily during cycling and then 25% every week or twice a week once established.
2. What size heater did you get? I specified mini because they are made flat to fit into a small tank. If you can, take a pic so we can see how it is set up.
3. Make sure you post ammonia readings when you test everything else. Did you get the API kit like specified?