I also had the same issue when I purchased that throttle tube.
The covering will not actually close as expected over the tube, thus binding it completely. I felt pretty stupid about it, and haven't gotten back to fiddling with it further.
https://www.amazon.com/gp/product/B005C59NO2
I guess I should also say, I pulled the cover out completely and tried putting it on the tube without any cables etc. It still wouldn't fit. The only thing I can figure is that they've sent us both the wrong tube.
https://www.amazon.com/dp/B005C59NO2/ref=cm_sw_r_oth_api_glt_fabc_YGG2B9FNBP2BPNT92RN5
That’s the one you need
Did you do it? OEM tube is here on Amazon.