On my coop I put the purlins 90 degrees to yours, so that those gaps were only 1/2" at most in that spot - my fear was mice being able to climb in through those holes. I would just cut some more of that 1x4 and stick them in there to close the gap halfway. If not, add some hardware cloth.
Keep in mind with the way you constructed your roof that the corrugated panels can flex with the way you have your purlins going parallel with the corrugation. May likely end up with a wavy roof in the future that could get looser over time.
I think it's not secure enough, and also question the support structure. If you get snow especially, those roofing panels won't hold up.
Rats, weasels, and raccoons can enter easily, day or night.
Mary