You don't really need a filler with that load. I don't shoot a .38-55 but have not used fillers in any Unique load in years. When I did, it was in the .35 Remington, which has sorta-kinda similar case capacity. Generally I'm into using Red Dot and Herco now, which light very easily and fill more of the case. Not to run down Unique - it's still a crackerjack powder for boolit loads. But if you happen to have any Herco, give it a try. Slightly slower than Unique so you'll wind up going up to 11 grains I'd reckon.

When I did use fillers, I found kapok to be easier to load than TP. And you're using way too much TP anyway. A 1" square would do the job just as well. Maybe better.