My quick tip for you, Caitlin.
You may have already been doing this, but for something like this you should be setting your aperture to what I’ve heard described as a “who cares” aperture. This would be about f/8 or f/11 (because you really don’t care about anything not being in focus). Definitely use a tripod (mine allows the head to come off and attach to the bottom) or something else to hold your camera steady, and don’t be afraid to open the shutter for a good long time.
Yes, get a speedlite! I don’t know the one @jamesstaddon is recommending, but I’ve got one that works well made by Altura Photo. An off-brand will work to get you started.