This is the redstone aspect of the TNT cannon, not yet the clock. This will be where the dispenser is later placed at and it also holds some redstone. Lastly add blocks in the position where the red wool is on the picture. This is a 2x3 field which will hold aditional redstone later. After you do this, add blocks in the spot where the green wool is on the third picture.

Also this time dont place your repeater next to the launching tnt, which is going to be at the fenct.

In this case this is not bad as the TNT is already primed when you put it in. Also you will move your whole row of these back by one from the original design so that the last TNT will touch the sourceblock of water. Each of the has to be between the orange blocks and one block above them as well. This acts as a color code so I can more easily show you which blocks I mean, in which case for you these blocks would be the ones you chose as your solid blocks. For the next step you will be adding some more solid blocks in the positions that you can see the orange wool in.

Minecraft how to make a tnt launcher