Get some black EPDM gasket weatherstrip from the hardware store. It flattens out to almost nothing and will give a nice finished look to any gaps if you take the time to line it up. Pretty simple. It has an adhesive backing. Splits down the middle so you only use one side. See link for picture and description below. I used it for an EOS front splitter on my C6 GS that had a gap and worked perfectly.
https://www.homedepot.com/p/Frost-Ki...25BK/202844545