The leaves are smaller when they are young. It takes 8 weeks for them to get to the blooming stage. If they are leggy though they may not be getting enough sun. Petunias require at least 6 hours of direct sunlight a day.

The non blooming may be your fertilizer. You may be fertilizing too much or have too much nitrogen in your fertilizer. Petunias only need fertilizer every 3 weeks and it must be a balanced fertilizer--15-30-15 or 20-20-20.
15-30-15 is a good all around fertilizer for most flowers and vegetables. A high first number means high nitrogen--great for lawns but no good for flowers. In flowers it will produce nothing but good healthy dark green leaves.

I grow them by seed and plug, and found one newer variety this year I thought would be exceptionally pretty, but their growth habit as only been marginally better than you describe. I'm wondering if your problem didn't come with the seed. The other varieties of wave did fine.