What is shown in the north indicates you aren't setting yourself up for success here. If you haven't done this a few times that is understandable.
First off, to take Leningrad, you will need three armies in the immediate area, one of which is a full, 20-21 CP army of guards rifle corps maxxed in SUs with sappers. The Finns won't be moved with less. You also need artillery divisions and supporting air. The Luftwaffe should have disappeared here by now, so you can bomb at will with the max # of IL-2s. Having 3-4 tank or cav corps to exploit into an enemy hex you might not otherwise get to is a good idea. Once the Finns defense is cracked open, they can't stop you.
As the assault on the Finns is underway, you have to understand what is happening elsewhere. What should be happening is your opponent is having AGN fall back, not to the west, but to the southwest so as to not get cut off. What you must do is not worry about going west, except for about 3-4 cavalry divisions. Everything should slide southwest along the ground you already control so as to max out your movement. Do not concentrate along that dashed arrow towards Riga, because you won't bag anything of significance here. Your direction of focus is Koenigsberg,and he will give up ground just about everywhere in the Baltic states. What you want to do with the 3-4 cav divisions is head for every uncaptured port. Once you reach them, large chunks of territory will flip to your control. This also means you will not have to deal with the logistical issue of moving entire fronts into what is essentially empty space.
Here is a visual of what things should look like.
