One item left

It depends on what ingredient you had to collect @ColleenMalleo

On some boards the items you need to collect aren't all available at the start of the level. When this is the case the missing items have to generate onto the board, and this is sometimes completed by a cannon, or a Magic Mixer, or by self replication.

If you have to collect chocolate then if you destroy all the chocolate on the board you will not be able to collect the required quantity as no more will generate

The same goes for Magic Mixers they sometimes produce candy pieces and if you destroy a Mixer too soon then you won't get all the candy you require to complete the level.

Which level are you playing?

Magic mixer or evil spawning machine. Looks like a washing machine with a spinner. They will spit things out at you after three turns that you take.