GenChem will up registration to ~300-350 per section.
Last years enrollment for the 3 sections were 196, 355, and 350. You'll get in for sure.
Same for the subsections. Worst case scenario is you /might/ get stuck with 9am, but you will get in.
I heard that they shut down the physics registration recently,
Huh? Not sure if I'm reading this right. Physics registration is not closed permanently. It's been that low since it opened back in April - to purposefully keep spots for freshmen. They only admit into 197 off of the waitlist. Generally each section will have ~100 students in it. Registration hasn't even opened yet for freshmen engineers (tomorrow morning I think?) - that's usually what fills it.
But just like chem, if you want to take physics you can... it just might not be the section you want.
[op I know you're already registered for physics, but I figured I'd still post that for others reading]