Do I get an extra draft pick if I don't keep the maximum number of players?

Yes. If you don't limit your draft to a certain number of rounds, drafts continue until all owners have filled their roster.

For example, if a team keeps 24 instead of the league maximum 25 keepers, they'll receive an extra compensatory selection at the end of the draft.

You can see this on your league's draft board (League » Draft » Draft Board).