I have a texture problem with the cubemap I'm rendering and can't seem to figure it out. I've generated a cube map with direct x's texture tools and then read it using

D3DX11CreateShaderResourceViewFromFile(_pd3dDevice, L"cubemap.dds", 0, 0, &fullcubemap, 0); 

The cubemap texture is not high quality at all and it looks really stretched/distorted. I can definitely tell that the images used for the cubemap match correctly, but it's not great at all at the moment

I'm not sure why this is happening. Is it because my textures are too large/small or is it something else? If it's due to the size of the textures, what is a recommended texture size? I am using a sphere for the cubemap not a cube.