I'm thinking the same hon!! It sounds like you should get a referral and get it checked out with a paediatrician, at the very least it will relieve your anxiety and worry about it if it all turns out okay. If on the other hand there is issue, you can get started on getting some help for your lil angel before he gets too much older.
The earlier the intervention the better outcome!!
Your boy sounds very similar to our son, and he went undiagnosed until he was seven.
The only indicators that we had from professionals at all was through our sons pre-school that he attended for 3 years and it wasn't until his final year before kindergarten that they mentioned to us that "our son has outgrown pre-school a year ahead of his age and that he was very very intelligent"
The anxiety was always there and because I went through a relationship breakdown from quite an abusive ex I wrongly put it down to the impact that this would be having on not only my son, but all of my children.
My son is also profoundly gifted and so he is so smart all of those early learning indicators were fine and he was reaching all of the childhood milestones ahead of schedule and his speech was very impressive!!!
He did all of the things that your mention in terms of playing, he would line toys up, was a very busy little bee, was outstanding at lego and complex construction, completing amazing projects that were some 8 years beyond his age level, following the visual instructions in the manual perfectly. He would do things like turn his three wheeler bike upside down and spin the pedals around for ages and ages watching the wheel turn, but stupidly, the penny didn't drop for me.....we knew he was different, a little different than other kids, but all kids are so very different and we just accepted him for who he was.
Our first major spanner in the works was his first day of kindergarten, we had a call from the school that very first day, because he just simply could not cope with the overwhelming school environment, there was just way too much sensory information coming in and the poor kid crumpled into a little ball in the classroom bag cupboard and pulled all of the other kiddies school bags in on top of himself.
Hope this sharing helps in some way!!!
Had we realised earlier we would have acted quicker but realise now that his giftedness actually masked a lot of the symptoms and unless you were familiar and aware of what ASD looks like, you wouldn't be able to tell.
From kindergarten it took two years to be diagnosed, with all of the testing etc.
So yeah, it might be time to get it checked and then you can be rest assured or be well armed with what you need to do for your lil man!!!