Just seems like the comet is taking up a fair bit of space in the image,
Ive just done a Stellarium simulation of your field of view and its stating 2 degrees, Id assume in horizontal, but no drama if 3 deg...
I have simulated my 135mm field and stellarium stating 6.8 degrees..
That said, all i can guess is that your chip is really small with super tiny pixels unless im missing something,,,
With all due respect