So I’m trying to model a car using this tutorial https://youtu.be/jcSDF917dBo
The mesh gets messed up and looks really weird. Not sure what’s going on here
There are several issues here – as @Matakani said, the file you shared doesn’t show the ridges you posted.
In what you shared your topo doesn’t match Jan’s – you have some extra bits hanging around, and 2 of your edge loops are connected towards the -Y (his are not). And as @oo_1942 alluded to, bridging edge loops creates very ugly topo if the vertex count doesn’t match, and here it doesn’t; all 3 lengths have a different count.
I’ve done some minimal fixing to show how it should roughly look (very roughly; more even topo is better, and I didn’t have the blueprints).
But it seems to me that to get the screenshot you showed above, you must have already gone further. So you need to share the newer file if you want us to find why there are those ridges.
However much I love Blender Secrets, car modeling is pretty complicated. I’d be looking for somebody who specializes in that and spends more time on the details of why one does things in certain ways.