Hi Denise, your backpack will be more manageable than other peoples bags, handbags, childrens backpacks, nappy bags, camera cases and laptop cases, you will just have one tidy item to pack away, so that is not a problem.
Re failing....you don't need to prove to anyone you can do this, although I kind of know how you feel, I told everyone I was going to do this thing and I would have been embarrassed had I packed it in during the first 2 days. As I was walking on my first Camino, fumbling along with getting to know my body and limitations and sharing my experiences via email with friends and family, most said I was mad and should just abandon the whole thing and have a lovely luxurious holiday instead. Even 2 or 3 days of walking was a huge achievement for most of them. Just getting there and getting through the first day is the first step of your achievement. Pace yourself well, listen to your body, take it easy in the beginning. There are overnight accommodations every few kms, so no need to fret. Just think of the next few steps and don't think too far ahead, it feels insurmountable if you do, but everybody can do a few more steps and focus on just that. I am a real neat and clean freak and really like my personal space and when I did the Camino that was the very thing that I knew would be the biggest challenge for me. I threw away my jandals for the shower after a few days, as I could not be bothered carrying them and coped fine in bare feet. I learnt to detach from what was going on around me in crowded dorms without having to leave the room. It is really liberating to face one's fears and we are all capable of doing it. Go well, and go with the flow, regards, Gitti