It is possible but I am not sure if it’s the best way to go for your problem.
From what I understand you only want to reconstruct the RGB image from the output, am I right? If yes, do you know what each channel of your output represents? Isn’t one of the channels the edge map?
In case you want to do that, you can either change the output shape of your 3rd conv2d or add another layer with the input channel of your last layer and your desired output dimension. But you may need to adjust your lost function as well depending on what loss function you are using.