My 2 DD's and I were there last April. There is so much to do in SF I didn't have time to sew a stitch. Depending on where you stay, if you are down town, you do not need or want a car. Buy yourself a pass for the public transportation - there is a pass that covers the buses, trains and cable cars. (Each cable ride is $6.00 even if you only go a block!)
Treat yourself a trip to Alcatraz, you need a reservation, so make it before you go. It is a walking tour and you wear head phones, so you go at your own pace. And you can stay as long as you want. There are bus tours, check out Groupon for these. We bought one that lets you get off and on for 24 hours. So we started in the afternoon, and went back the next morning. We had a wonderful time at the waterfront. And we had a great walking tour with a man that took us around the older part of SF and he had great stories. I wish I could have gone on his tour of the bakeries, but we ran out of time. I did have one complaint of Ghirardelli - the ice cream sundaes were too big. My DDs had to finish mine.
I understand that you will be traveling alone, but these are things you can do on your own. I kind of like to go at my own pace, stop where I want, which is not always possible traveling with others. Do you have a cel phone? The Google Maps app will tell you how to get around using public transportation, it was great.
I didn't see any fabric stores downtown. We didn't look for them since neither of my daughters sew.
I hope you have a great trip, San Francisco is a great city to visit.