ffmpeg - how do I remove these strange white boxes underneath my drawtext?

Question

After working all day on this, I have my script working ALMOST perfectly:

ffmpeg -i source.mp4 -filter_complex "[0:v]pad=iw:ih+1680:0:(oh-ih)/2:color=black, drawtext=text='SPENNY FREAKING OUT ABOUT TO DO':fontsize=190:fontcolor=white:fontfile='/Windows/Fonts/Impact.ttf':font='Impact':line_spacing=30:x=(w-tw)/2:y=(800-th)/2, drawtext=text='HARDEST WORKOUT IN THE WORLD':fontsize=190:fontcolor=white:fontfile='/Windows/Fonts/Impact.ttf':font='Impact':line_spacing=30:x=(w-tw)/2:y=h-450-(th/2)" output.mp4

This adds padding above and below the video, and text is added on top of the padding.

But I have a few little problems that have been holding me up for hours finding a solution:

1. How do I remove these strange white boxes? Screenshot Screenshot 2
2. Is there any way for me to align:center the drawtext? As you can probably tell in the script, I'm using a very crude method - adding blank spaces as characters so that the text looks centered.
3. I'm also having to manually press ^L (Ctrl+L) in the command prompt to create a linebreak, for some reason \f and \v don't work. Can this be somehow automated?

The first problem is the most important. 2-3 I have workarounds so no big deal, but it would be nice to streamline everything.

Thanks! Hoping someone can help me!