How can I improve the shape/appearance of this bread?
Before we start on what might have gone wrong, let me assure you that you obviously are doing a lot of things right:

You have surface tension in your loaf and good oven spring, meaning you got the shaping right and seem to put your bread in the oven at a good time during the final rise - my guess would be "slightly underproofed", which is exactly what you want for a wheat bread like this one.

With your slashes I suggest that you dump the X-acto, because the blade is too short. The classic lamé is one possible route (and can be easily substituted by an oldfashioned razor blade on a chopstick), but you probably need a few more loaves to get the hang of using it - you need to work fast and the bent blade and thin handle is different from what you are used from kitchen knives. A serrated knife is a viable alternative, provided it is quite sharp. Whatever you use, you don't want to use a "sawing" or "zig-zaging" motion, but just one quick swiping movement per slash.

The higher the hydration the more likely is your slash to seal itself again, simply by the weight of the dough. Therefore an almost horizontal slash is recommended. The idea is to create a "flap", not a "valley". The thin flap will become the "ear" as the two overlapping parts drift apart due to oven spring. For a loaf like yours, I personally aim for a cut of almost an inch. This is no hard and fast rule, every dough and bread type is different. Once you get the basic technique right, you can experiment.

Note that the bread will expand perpendicular to the cut, so diagonal cuts should be always oriented mostly along the long axis and multiple cuts should be running parallel for quite a bit. More crosswise cuts will create the "bulge" that can be seen on your loaf, almost as if the loaf "arches its back".

Good steaming will keep the crust pliable, so that oven spring can open the slashes well.