I did a ton of work finding the midwifery practice that gave me the best possible chances of a peaceful, natural delivery and then wound up with an emergency section due to previa.
While I was pregnant, I felt like I wanted to bury my head in the sand so very badly. I wanted a natural birth, I was terrified of surgery, I knew I was probably not only going to have to go to the hospital, I was likely to wind up at a different hospital than the one I'd carefully researched and selected, at an institution I'd rejected for having insufficient regard for natural birth. And in the end I did end up at that rejected hospital, and their level of regard for natural birth was totally irrelevant. They have a great NICU, which we needed badly (DD was born at 32w 4d).
1. Not all complete previas are created equal. There are complete previas as illustrated on the internet, with the cervix centered on or near the cervical os, and then there are complete previas where the cervical os is completely covered by one end or edge of the placenta, and the placenta is actually centered higher up. This last kind is far more likely to politely go away.
2. If they've identified a suspected previa at this stage, they should be scheduling you for a follow-up level 2 ultrasound sometime between 28 and 30 weeks. If they haven't said anything about this, push for it.
3. It is possible to have an informed and empowered experience of even an emergency c-section - start taking those reins now. If the previa resolves, you can drop them.
At my six week follow-up appointment, I made the OB who did my surgery tell me what had happened to me, and why I had hemorrhaged. She told me some things I wished I had known earlier - when the placenta is implanted over the cervix, it tends to irritate the cervix, causing dilation. Dilation, in turn, irritates the placenta, and can cause rupture of the lacunae of blood in the placenta and damage to the oxygen-transfer membrane between mother and baby. This can cause really dramatic bleeding and some serious health problems for both of you.
Practitioners vary in their recommendations regarding how much and what kind of rest is appropriate for patients with placenta previa, and every woman and every pregnancy is different. No one who hasn't met you can possibly tell you with any certainty what you should and shouldn't do. What I can say, what my experience leads me to strongly suggest, is first that you get help now (who would you call to come be with your kids or to take you to the hospital if you started bleeding? what can be put in place in case you need to be on bed rest, or have an extended hospital stay?), and second that you respect your body's limits. If you feel tired, rest (I totally sucked at this part). Be more than usually vigilant about your hydration and about contractions.
The longer you can stay pregnant, the better it is for you and the baby, and the higher the odds that the previa will resolve.