Final Cut Pro, Gaps, spaces between clips

The magnetic timeline should close the gaps when you shorten clips. Perhaps you're using the Position tool.

To find the gaps use the Timeline Index. Search for gap and when they are listed to can select them all and press Delete. It will move things around so check that all the elements in the project still have the correct timing.

In addition to what Tom said: are you perhaps working on connected clips? When you say gaps, do you actually mean gap clips, or just intervals between successive clips?

Perhaps if you post a screenshot it will become clearer.