It is difficult for me to assist you without being there with a one-on-one instruction, but, if you will concentrate on not casting a fly rod and, instead, concentrate on unrolling a fly line behind you on the back cast and unrolling it in front on the forward cast, it will help you to better understand the techinques of using a fly rod. You cast a spinning rod and a casting rod, but, you unroll fly line with a fly rod. Look at your back cast and watch your fly line unroll and do not come forward until it has unrolled behind you and then bring it forward and let it unroll in front of you before lowering the fly rod. This takes much less effort on your part.

What rainbowchaser recommended, with sitting in a chair, is good advise because when you are in a canoe, you are closer to the water and you will need to concentrate on holding the fly rod and line up higher on your back cast or it will hit the water behind you.

The above is offered as help. Most people are just too agressive with the stroke with the fly rod and do not allow the fly rod to do the work for you. A nice slow movement of the fly rod back to a stop and then a slow forward movement of the fly rod to the front stop is all it takes. The backward and forward movement should be a smooth movement with no agressive push of the rod hand coming forward. Just one smooth stroke back and forward with a short wait for the line to unroll behind you and in front of you is all it takes. Most try to really push the fly rod on the forward stroke thinking this is the movement needed and it is not.

Just trying to be helpful and nothing more.....