If you have enough room, can you put a thin piece of wire around the line and twist it tight? I've done this on other fuel lines when i didn't have a clamp to fit.

A search turned up fuel lines and clamps for model engines. Now to find a hobby shop and look at what they have to offer.

You have the wrong line.

I agree with tomplum.
You need to get the inside and outside dimensions.
If they are not correct this is the problem you will have. Also if the outside diameter is wrong you will have the gas leaking from the tank.
Solution is to get it from the manufacturer.
I do see some good deals on ebay.

I did get this fuel line from a Husqvarna dealer. He has since closed and no other is convenient for me. The line fits fine except for the one (of two) tubes on the priming bulb. I will measure both of those tubes. If one is smaller, then the other end of a smaller line will be a problem for the tube on the carburetor- where the present one fits fine.
On the Internet, I did learn that the silicone fuel line used often on the model engines is NOT suitable for gasoline.

A good saw shop is your best bet. You could try the clamp approach, but you seem to indicate that it is looser than should be. It is many time just easier to have a shop install the line off the roll imo rather than buying the short pieces and then trying to feed the line and filter through the tank opening.

When I have had gas line problems I get my caliper and take the true dimensions. The return and supply lines are almost always different dimensions.
And just because the outside looks correct can once again mean gas tank leaks.
From what you are saying you need a smaller id hose. I have never never needed a clamp.
To make your life easier I would suggest to go to a Dealer and get the Original parts.
One of the best kits on the market is by Ryobi. They sell the hose, filter and wire to pull in the gas tank hose.
The pull wire is a excellent tool.

I used the wire as nod702 suggested and it seems to hold much better. Extensive use will show if it really is effective. The model engine clamps may be a good solution- I have located some of them. And I thought of using a short piece of shrink tubing over the fuel line end and shrinking it with a heat gun to act as a clamp.
About the line size- the stem on the priming bulb on one side is small- the problem side. The other end of that same line goes to the stem on the carburetor which is larger. Husky may well have molded the original fuel line with different end diameters. The dealer tells me that Husky warns against ethanol for their equipment. But it is virtually impossible to find gasoline without it. So buying original is not a good solution in this case.

Mebbe apples and oranges, but.. When I had trouble with my 5 yr old Husqua string trimmer. It turned out to the fuel line. Loews, all places, sells it 2' for about 2 bucks. Exact size and material.

Yah, the original gas line split inside the tank on its way to the pickup. Since I have been adding a cap full of Marvel Mystery Oil to the tank when I fill up, my troubles with 10%ethanol gas have pretty much stopped. What I think is funny is that my 35 yr old Stihl was designed to run on leaded fuel, the once clear line is ivory colored and hard as a rock. Stihl runs fine. it even has its original points set. The new gas doesnt seem to bother it. But it messed with my old OPE something awful. Until the MMO anyway.