A key tool when using flex containers is the justify prop (equivalent to justify-content from regular CSS). It's the way to "anchor" components at different ends of the container. If you then want a little space so things aren't right at the edge of the page, that's where you can add padding to the container's style.
image borrowed from the above guide
Also, it sounds like you might have too many items in one column or row container, causing things to wrap around in ugly ways when the page resizes. If you want to prevent that you have to manually put things in row containers and turn off wrap.