In my opinion, making A2 autotiles is one, if not, the hardest thing to do. Because making them look seamless and good on a big surface is difficult to achieve and they are so important, defining the look of your map. I know, I struggle with A2 myself.
So, don't despair, if you don't get it right at the first try, it takes a lot of trial and error. Especially with a natural stone look.
I made some lines in here, compare it with the original. I marked some very visible lines in your pattern that makes it look tiled. One, because they have darker edges, but more importantly, because the stones are arranged in horizontal or vertical lines, meaning the height, size and lineup of them is almost the same. You only change this if you change the pattern.
And if you want to make it close to mv rtp, I can maybe tell you that the single stones there are bigger and it is done with pixel art/painting (meaning, probably with a pencil and not a big brush). So, you would need to change your lighting technique.
But it will already help you, looking closely at the vx/ace rtp. Study the A2 stone patterns and how shadow/light was used in them. Most of the time you have dark spots between the stones, sometimes like a dark ring/edge around one stone, then a bright edge color and then in the middle the middle color. You've gone the opposite route and just put a bright spot in the middle of the stones. Try switching that to bright edges here and there and with darker spots in between the stones. I would recommend using a pencil tool with low oppacity.