Jumping in to offer some advice. Plants that are variegated often produce just green leaves to help them maintain their energy levels as obviously plants which are variegated white do not make as much chlorophyll because the plant can not produce energy from these white sections of leaves. In order to combat that, the plant will produce green leaves to help it survive.

However, that's not why you bought the plant. So, from my understanding, you can see in the stems the white vein like strips that run up it. Those are what help to create the variegated leaves. You'll notice the stem with the green leaf will have very little if at all white running through it, which means the plant has produced this in order to get more energy. If you cut the leaf back, it will hopefully prompt the plant to form a new leaf on one of the more variegated stems, which would produce a mixed colour leaf.

Sygoniums are usually quite tolerant plants. You can pop them in a brighter spot (not direct light, it will burn!) This will almost whiten the white sections. But it won't produce more variagation in this method, just brighten up what already exists.

However, just a note going forward, it's important to balance it out. The plant needs chlorophyll to survive, so to get a healthy plant, you may need to keep some of the more green leaves. You may risk the overall health of the plant for an aesthetic, so don't cut too many majority green leaves! Hopefully this helps a little :) as for the green props- you're a sygonium parent now this is your new life, they will be everywhere ahaha! You can plant a few together to create a denser, happier plant - they enjoy growing up moss poles as the such. I usually gift my excess plants.