Construct Mesh problem

Hi everyone!

First of all, I'm sorry if there's topic like this but i couldn't have found one. I've wanted to do a low-polygon project. But I have a problem with my algorithm even though I've done everything like in the example from the Internet. I have been trying to use this algorithm on a few meshes, but there's always those three errors. I'm putting here the example that I've used and mine errors.

Thanks for every reply.