You seem to be confusing your Spell Slots and your Prepared Spells-- which is a common mistake! Your Spell Slots are how many things you can cast before you need to take a long rest.
Prepared spells are the spells you have memorized for the day. As a Druid you can prepare spells equal to your Level + your Wisdom modifier. So at level 5 you will be able to prepare 5 + your WIS mod spells each long rest (I'm assuming you have a 16 or 17 in Wisdom, as you have 8 spells prepared), which you can cast using spell slots of the appropriate level (you can cast 4 1st level spells).
Here is the text from the Druid class Spellcasting feature which also explains this:
For example, if you are a 3rd-level druid, you have four 1st-level and two 2nd-level spell slots. With a Wisdom of 16, your list of prepared spells can include six spells of 1st or 2nd level, in any combination. If you prepare the 1st-level spell cure wounds, you can cast it using a 1st-level or 2nd-level slot. Casting the spell doesn’t remove it from your list of prepared spells.