Build a mental checklist of your application: GPA, MCAT, letters, research, general volunteering, clinical volunteering. Recognize your letters of recommendation are the hardest part. Securing a letter is not the issue. You want a strong letter because a lukewarm letter is a bad letter. You need to be the person someone would immediately think "this is clearly a successful person".
At the end of this year, you start writing your applications. Applications open as early as May. In a way, whatever you do this year marks the final additions to your application. Most of your accomplishments should be done right now.
You don't need to take a gap year, but by the time I talk to many people, they have already decided to take a gap year.