Once you have drawn all the pins, you can draw a box (keyboard command b) to define the chip boundary. Don’t worry too much that your chip does not look like a chip, as it is a symbol in schematic capture.
Also, use the keyboard command et to “symbol translate”. This defines the origin of the symbol as the lowest-leftest corner of the visible part of the design.
Then, save the file. Be sure to save it in the folder where you have designated for your own symbols. You can also move a symbol file to the designated folder later. The file name of a design should end with the .sym extension. The convention of the file name is to use all lower case characters, with a dash separating the name of the component (probably the same as the device attribute) and a revision number. If the design is footprint specific, also add the footprint as a part of the filename.
After you add a symbol, you need to close gschem and restart it for the new symbol to be accessible.