art mock exam disaster

I had an art mock exam on Wednesday and Thursday and it couldn't have gone worse. I stupidly chose a very detailed pictured to paint( as the photos I took for the theme were terrible and I had 0 ideas) within the 10 hour time frame (we still get time afterwards) and I managed about 5% of it, as I can paint but it takes me so so so long.

Everyone else was basically done and I was the only one with a mostly blank painting. I can't even count the amount of stern talking to's I got from teachers, it was so unbelievably embarrassing. I don't even know what to do because I know I will never get this done by February, (picture really is just that detailed) which is when our coursework mark is sent to the exam board. But teachers are taking them in now to mark (for our reports), but I haven't even done a quarter of it.

On top of that I have other coursework for art and a new theme we have to apparently work 2x the speed on.

Does anyone know what I can do? Also any tips for choosing a doable picture for your personal timings for the real exam?