I have a 42 inch ripping chain on a 42 inch Oregon power match bar and the chain needed a little persuasion to go on. It seemed to function normally when I powered up the saw and milled a couple of slabs. No cause for concern then?
The chain will stretch. Next time I doubt that you will have any trouble. Sometimes even a new sprocket coupled with a new chain will make things a bit tight.
As long as the tension is correct when it is installed that is OK. It may be a drive link short so with the bar all the way in the chain is still a tad tight? Or the new sprocket/bar/chain just need to break in a bit. With that many links it will stretch after running for a bit.