Trying to increase the size of my hard drive, Error: -69771: The target disk is too small for this operation
I have to quit applications because there is not enough free memory

Free memory is not hard disk space, but rather RAM. You can resolve this by quitting apps that are using lots of memory. You can find which processes are using memory in Activity Monitor.

If you're still interested in making more disk space for other reasons…

a gap is required in your partition map which is missing or too small

This is the actual error. diskutil list shows an APFS container disk0s2 of 70 GB, and a HFS partition disk0s3 of 180 GB.
70 GB + 180 GB = 250 GB, which is the total size of your disk — there's no free space gap to resize your container into, it's as big as it can be.
You can remove your HFS partition disk0s3 (back up your data first), then expand your APFS container into the gap created by that operation.