My heat gun is listed as 590 degrees C. (Grizzly 1800 W) I think your gun should be up to the job.

Is the wood moist from soaking or from steam?

Have you tried some proven bendable woods like oak, ash, or even pine?? I have no experience with spruce.

Are you letting the gun warm up the section you want to bend for enough time for the heat to soak through the wood? I use about a minute of heating 1/4 inch thick pine before trying to bend it... about 1/4 of the time on the outside of the radius and 3/4 of the minute on the inside of the radius.

My experience is that when it gets to the right temperature, it bends a little like ... taffy. Put a "french chew" in the freezer for an hour and then begin to warm it with your hands. It is hard as a rock, 30 seconds later it is hard as a rock, 30 seconds later it starts to bend just a little, then really bends well, then 30 seconds later it falls apart when you try to bend it.

Wood does just about the same thing... It splinters when you try to bend it, then begins to bend pretty well, then gets warm enough that the inside surface of the wood buckles in a fracture. The goal is to get the wood to that bendable temp without getting it so hot it buckles.

If you want to do some cheap practice, I can pretty well guarantee that regular construction pine if cut into a 1 1/2 inch x 1/4 inch strips (slices of a 2x4) , if steamed in a homemade steamer for 2-3 minutes will bend rather well for almost a minute. If there is a knot, or a sudden change in the grain, it will probably break, but a lot of bending practice can come out of one $2 2x4.

I'd use heavy leather gloves, like welding gloves, so that you are not afraid of getting your hands in full contact with the wood. Later you man not need the gloves, but they are a good learning tool. Expect to put about as much push into the wood as you would if trying to pull an arrow back on a bow. And bend the wood around something round and about a foot in diameter. You can use a special form you build, the coaming edge of another kayak, or even (my favorite) the steering wheel of a riding lawn mower. If the grain wants to splinter on the outside of the bend, turn the wood over and bend it the other way - or use a leather belt on the outside radius, or just let it split and then look at the grain afterwards to learn what grain run out means to bending in that species of wood.

After you can bend the wood with steam, then try it with the gun. The heat gun will heat the wood the same way, but its heating is much more local. You bend an inch or 4 at a time with a heat gun, not the whole piece. It bends in the same way, so practice with steam will give you the feel of what the wood will do.

Let us know how you do.