mbp hdd problem

I had 2 partitions, one uses windows the other is the mac. In disk utility under partition tab, I pressed delete on the windows partitions and now they're not on the list but the space it uses up, which is around 70gb did not merge with the mac partition - my startup part.
How do i remerge this with the mac parition.
The hard drives aren't there on the list on the left of the disk utility and when I try to use first aid, I have a few errors.