I've tried turning off snap to pixel as suggested by someone in a similar thread but it didn't work. Does anyone know how I can resize this without messing up all the lines?
Before resizing, deselect all and double click the Scale Tool → uncheck Scale Strokes and Effects and Scale Corners:
Select your artwork and scale it.
Additionally, you can set this to be default in Illustrator's general settings.
Edit → Preferences → General or using the shortcut Ctrl+K or Cmd+K