With a mallet, all things are possible. This is a rough cut, cedar garden bed, so be prepared for some splinters, both along the boards and in the channels. However, with a bit of mallet work, those splinters work to your advantage - they help keep the boards in place and square while setting this up. My advice is to build two short corners with a single plank first, then do the two long sides and other short side with a single plank. Ensure you have your bed in the right place, then add the upper planks. A framing square helps, but is not strictly necessary. Be aware that, as with any wood product, some boards may warp with weather and will swell when exposed to humidity. If that doesn’t work for you, you want a Trex (plastic) raised bed.

I’ve lined mine with cardboard, since that will biodegrade slowly while also smothering any weed seeds under my beds.