“Check Hybrid System” after cleaning HV battery fan… where do I start?

Cleaned the HV battery fan in my 2010 Prius yesterday. I followed this instructional video at first, but I switched partway through to this one from NutzAboutBoltz, which seemed like a more efficient process that required less trim removal.

In retrospect, switching videos just added confusion during the reassembly process, and two problems have come up as a result:

1. As a newbie amateur, I didn’t develop the best system for organizing screws, bolts, etc. beforehand, and I had a couple small mixups with replacing things. I think I eventually got everything back together alright, but I’ve got this extra Philips hex head screw and washer (see picture) and I cannot for the life of me determine where it came from. Anyone have any ideas?

2. A much bigger problem is that I tried powering on the car after reinstalling everything and got the “check hybrid system” warning on the dash. Tried switching the car to Drive and heard the ignition switch click, but no engine start. Without the engine running, I cannot run my BlueDriver OBD either it seems (not entirely sure if that would even be helpful here tbh). Upon inspection, I realized I hadn’t fully inserted the HV battery safety service plug, so I removed it fully and then reinserted it fully. Still didn’t get the car to start.

I can’t afford to **** this car up, so I’m just checking: how should I proceed? Should I check fuses first, or remove the trim again around the HV battery fan and check that everything is in order? Does the car just need a jump, or is my hybrid battery now a goner? Lol I’ve searched the forums but have seen many answers and am not sure how to prioritize the potential solutions I should try.

 

It’s my understanding that it’s the hybrid battery, not the 12 volt, that starts the ignition, no? Not entirely sure what the relevance of the 12-volt battery is here; my lights all work just fine right now as do all the other 12v-powered accessories.