As a rough guide, until they reach adult mice, the food needs to be around 1 1/2 times the width of the snake's body and leave a visible lump in their belly for 48 hours after feeding. Once the lump goes down within a day, then it might be time to offer the next food size up (as long as it's no bigger than 1 1/2 times the snake's body). Once they're on adult mice, most won't need anything bigger for the rest of their lives.
If you look at your aginst the rough guidelines above and think it needs to go up a size, you could offer it 2 pinkies at a time for the next feed. Personally I'd stick to feeding every 5 days - I think it's about right for either single or double pinkies.
Comparing Corn Snake growth rates is a quick way to go nuts! They grow at such different rates, even on the same feeding regime. Some put on length first and then fill out when they hit the "teenage" stage. Others grow in proportion and put on both length and breadth - these are likely to be slightly shorter when younger and catch up as adults. Just because someone else has a Corn the same age on fuzzies, doesn't necessarily mean that it's right for yours. You have to make a judgement for yours as an individual. It's absolutely fine for yours to be a different size and be eating a different size of food.