Welcome to the forums!
Was this shape drawn with the Line tool? If so, that would explain what you're seeing. To create a shape, you'll want to use the Pen tool. The "Drawing your own shapes with the Pen tool" page in the help menu material has some good starter info on how to use it. (Happy to answer more questions here, of course - just know that we spend time on the forums as we're able to on top of our other duties. For need-answer-now stuff, calling (800.315.6664) or
emailing will get you a quicker response.)