Running an even bead on the edges of copper foiled projects is often difficult. Several things can help.
Hold the panel vertically and ensure the edge you are applying solder to is horizontal. This means that you have to keep moving anything that is not rectangular.
To apply solder and move the piece ideally needs three hands – one for the solder, one for the iron, and one to manipulate the piece. Failing such an evolutionary leap, you can use a small vice to continually alter the angle of the edge, you can get a friend or colleague to manipulate the panel, or you can place the solder so that you can pick up little drops of solder and place them on the edge. With practice, you can pick up some solder and transfer it to the edge before the previous dot of solder has cooled, so leaving a smooth bead by the joining of the dots.
Alternatively, you can place dots of solder near each other around the piece. You then come back and with one hand manipulating the piece the other can use the solderimg iron to heat and join the dots.
You do have to be careful that you do not move the panel before the solder has hardened, or it will run down the newly created slope to the new horizontal edge.
I find that it is much more difficult to run a bead on an edge than it is to “pat” the solder dots. This patting motion allows the solder to join together, but does not heat such a long line that it flows as you turn the piece to keep the edge currently being soldered horizontal.