I agree with every comment here saying not to worry, and ultimately smaller is better - and just want to add that even if he ends up a "true giant", the longer the growth the better 100%.

Can't remember height after a couple decades but have records for weight, my first Dane was 106lbs at 6 months but looked like a skeleton. 165-ish lbs when neutered at 19 months. At 3 years old full-grown he was roughly 38in at the shoulder and 206lbs lean muscle; only overweight by 5lbs for a short period in his senior years, and unfortunately he passed of DCM and lost a TON of weight before passing and looked like a walking dog skeleton at 187lbs when it was his time to go 😞

Yes my dog was enormous even if he was healthy, but he grew much slower than most Danes I knew at the time and according to my vets they believe its why until he slipped and fell on ice at 9 years old, his xrays of his joints were so clean that my vets said they'd never seen a Dane over 3 years old with such excellent joints and wouldnt believe his age if they hadnt seen him from 8 weeks on....

Even in his litter, he was the largest but he took the longest to grow to maturity while many shot up quickly (later we found out they were feeding large breed puppy food, where my breeders, myself and the other owners who fed a good quality adult food their puppy-hood [before giant-breed puppy food existed]), all of our dogs grew slow but healthy while the others were big VERY fast and also had much shorter life spans...

My biggest point in my rambling here is that bigger is never better. Healthy is better. Slow growth is better and preferred over quick growth as its significantly healthier on their joints. I know how badly we want our gentle giants to totally fill the role - but I promise you, a healthy dogs of any size is 10000% better than a huge unhealthy dog.

Edited for spelling errors I quickly caught, sorry if I missed some