How about sharing the SKP file. It’s difficult to tell what the profile looks like.
Best guess from your screen shot is that you’ll need to draw a face at the miter angle and intersect it with the frame member.
By the way, as appealing is it might be to apply textures to your model as you go, it’s better if you hold off on that until you have the modeling done. The textures can make it difficult to see what you are doing.