Jeremy,
The image has a JD of …384.896.
Gary Poyner has, I think, taken the ultra wide field ( Y Slooh in his nomenclature) scope image from the same run and obtained Mag 11.6 (V) so that is reassuring. He has done the same the following night and obtained 12.3 .
Mazin has marked star 113 as the nova and given different coordinates to VSX. VSX gives 17 39 57.08 -26 27 41.9.
The nova is close by and very red towards 10 o clock.
Direct measure of the brightest pixels in my image gives
V4370 113 128
11,000 21,000 4000
So I think around Mag 12 is about right for Mar 15.9 but means that there is a two mag difference in V between these results and those from some experienced observers. This is a situation that is unsettling and probably has to do with the redness of the nova. I have not reported my results to AAVSO.
Stewart