Welcome @Flossy,
The demons in the head is possibly the hardest part. One minute it's like Yep. I got this" and the next your scared stiff and howling your eyes out.
Our brains do like to conjure up the worst case scenario for reasons known only to itself and all the waiting around at the start just does your head in.
I had similar to you. No lump in the breast could ever be felt by anyone, thankfully it couldn't escape the MRI. I had the same surgery lumpectomy, aux clearance (5 nodes involved). ER+ PR + Her2 neg. 6 mths chemo and 30 rads. I had felt the lump in my lymph nodes so I had a fairly good idea of what it was going to turn out to be. Still horribly shocking though. It's all so hard to believe when you feel perfectly fine.
At the beginning it feels like it's going to take a lifetime to get through. Time travels fast and you're so busy with appointments and treatment, hey presto, and you're out the other side before you know it.
I did pretty well through chemo, kept my hair with the cold cap and had next to no problems with rads. It does suck but sometimes it's nowhere near as horrid as what you think it is going to be.
Keep chatting to us, everyone here knows how you are feeling.
Enjoy your holiday lovely.
xoxoxoxoxo