TPA0253: Help Understanding Mono Output
If I was to use a single speaker without a headphone connection, how
would I draw the schematic


Page 2 of the data sheet above shows you how to do this (see above).
Or if you want to use your schematic look for the nodes Lo/Mo- and Ro/Mo+ and connect the node called STEREO/MONO to Vdd via 100 kohm.