The problem is that your model is too small, SketchUp snaps to the nearest endpoint automatically if the distant is very tiny, also the lines that you want to be filled with a face, are not coplanar, that means that one or more end points are not aligned to the same axis or plane, the main cause of this modeling issue is having length snapping enabled. Fortunately, there are solutions to all your problems, the first one would be scaling the entire model by 100 times or more if it’s too tiny, that will avoid the auto snapping, disabling length snapping will prevent to create non coplanar lines and will improve the accuracy measurements of your model.
You should try the Dave Method and work on meters as if they were millimeters.
also, the straight lines don’t bend they just snap to the closest snapping point, but they´re still straight lines, it is possible to bend lines or almost anything on SketchUp but it requires more steps than just drawing a line.