Could being pregnant make my scoliosis more severe?

Possibly. The normal curvature of the spine does change a bit as a result of pregancy. Normally the thoracic and lumbar spine curves become more prominent during pregnancy - and usually returns to normal after delivery. It would be reasonable to expect that your scoliosis would respond similarly to the stresses of pregnancy and worsen some as well - then also possibly return to the prepregnancy state.
Doubtful. It is never a certainty to know for sure that the added weight of a baby along with the hormone relaxin secreted near delivery which can help loosen the ligaments of the pelvic floor to be able to deliver wont affect your scoliosis. It really shouldn't change your curve to any significant degree.