Generally the third grand prize is only available 2 ways. 1. paying money (either buying delicacies or buying the event building that gave you more snowflakes), or 2. spending most, if not all, of your snowflakes on double-days. And that also assumes that you're generally picking the box that gives the most delicacies per snowflake.
Its a trade-off. You can get the third grand prize, which is usually really great. But you might not be able to get all the daily prizes you want.
this made it a waste of time by not being able to collect the last 1 because of not enough snow flakes...
I know it can be easy to feel this way, but it wasn't a waste. You probably got a ton of great buildings, instants, and set buildings that will help your city. Be proud, and now in the next event you'll know more of what to expect.