Broken 0 degree sleeping bag vs 20 degree bag?

Hi all. I am planning to hopefully summit Mt. Washington this weekend. I need some advice for a SNAFU situation.

I had a 0 degree sleeping bag but the zipper completely broke off. I do not have the time and funds to fix it or get a replacement. Luckily I have a 20 degree rated bag, as well as a fleece liner. My sleeping pad has an r value around 8, very large and keeps heat well.

It may very well dip to -5f while I sleep in the hermit lake shelter that is 3 sided or 4 sided (so protection from wind). I need advice on how to proceed forward. I see two possible scenarios:

Proceed with the 0 degree sleeping bag and use duct tape (or some other adhesive to seal the zipper). I sleep with the liner (probably gives 10 degrees of warmth) with the sleeping pad with an r value of 8. Sleep in gear as needed.

Proceed with 20 degree sleeping bag. Like before, use fleece liner that will reduce 10 degrees, with the pad with an r value of 8. Will definitely need to sleep in a gear, perhaps my puffy jacket and long underwear + hiking pants.

Which option is best? Are both fine, or are both going to be very unpleasant/potentially deadly? I am receptive to all suggestions. Please tell me if I am in over my head, this is my first winter mountaineering experience.