It’s been a while since I did it with my classes, but we never used the flame spreader. We just adjusted the burner for a good, hot flame (blue cone) and had at it. The kids used to bend the glass into very elaborate shapes quite easily.
Is it possible your tube is silica (aka quartz, fused quartz, SiO2)? Such tubing is popular for more critical applications including high temperature ones. It has to get very bright before it will bend.
I’m not sure how to tell the difference. I think silica is sufficiently harder than borosilicate glass (Kymax and Pyrex are brands of borosilicate) to scratch it.