I HAVE almost FINISHED it. There are only a few things I'm working ON. Two separate, independent sentences. "have finished" is the present (have) perfect (finished) tense. It is used when something/action began in the past and is continuing. I know it is continuing (not finished yet) because you wrote that it was "almost" finished, and that means that you are still working to finish it. "working on" is a phrasal verb (a verb + a preposition). People 'work on' things such as projects or assignments or tasks. For example: Question: "Have you finished your work? Answer: "No, not yet. I'm still working on it."

I would say I've almost finished it, there are just a few things I'm still working on.

"I've almost finished it; there are only a few things I'm still working on."