is the wedding band supposed to match the engagement ring?

Traditionally yes, the wedding ring has matched the style of the engagement ring and this is still the most popular choice. However there has been a sharp rise in popularity of 'stacker' rings and brides are now often choosing a different style the wedding ring and then a third style for the eternity. Ultimately it's your decision and whilst it's nice to consider tradition, you're free to choose the design that you like best.