Accessory mount extender for curved bar: stem bolts vs double clamp
Most batery lights can be tilted a few degrees. The mount of your Spanninga light looks exactly as if it may be tilted as well. Check by removing the light, and look for a screw inside the bracket. If there is one in the centre, sligthly loosen it, tilt the light, and tighten again.
If the bracket cannot be tilted, consider to return the light. It appears you bought it most recently and might still return it. Then get one of the countless lights that can be adjusted properly. That will be cheaper, nicer, and more reliable than improvising a mount that fits.
I do not recommend to mount anything to stem bolts. That may work well, however, in the slim chance that it doesn't the consequence could be serious. I rather do not introduce another source of failure to fasteners of my bars and stem. If you need it at the stem, get a stem with a dedicated light mount. They are available in limited sizes and tend to be expensive premium products.
A utility bar clamped with two clamps will be even more difficult to mount as they would mount to angled bars.