Well done - on getting so up close and personal on the H and showing its inner detail.
I have seen another image on a 180mm aperture, which suggests an even shorter exposure of
1/60th* of a second would help. And of course the atmosphere has to be in your favour so close up. I'm looking forward to the next one with 2X TC
Best
JA
* Actually thinking on it further, you had a 0.65 reducer in there in your image, so removing it in future you'd loose ~1EV and also if using the 2X TC you'd loose another 2EV, so your original exposure time of ~1/15 th of a second (63.5ms) may be OK as it would certainly be dimmer (1/8th the light per unit area compared with your original setup) and may help overcome the oversaturation issue you raised. Perhaps even 1/8 th or 1/4 sec or bracket the exposures. Have fun.