Take some rope and run it around the pulleys like the belt. Have someone hold the tensioner then mark the rope. Take the rope out lay it straight and measure it
That really makes me think this belt is too short then if you have smaller pulleys and your belt is longer than the one supplied. Sounds like it’s not even a little too short it’s way too short for oem components just going off that comparison. I’ll try to the rope trick just out of curiosity