As you learn the cars quirks you will slowly become more efficient.
EV mode is much more efficient below 50mph, slower the better
Gas mode is somewhat complex but generally more efficient at 40mph and higher with a “steady foot” coupled with no stops.
Since you have L2 the following is very useful in cold weather
Burping - the key to Voltec bliss?
Ari_C is the guy
Over about a year I optimized my twice weekly long trip to be 10 miles shorter, mostly lower speed but only about a half hour “longer”
Following that path I can get up to 72 miles EV summer and only use 0.56 gallons of gas on a 100 mile drive.
Generally when you increase your real EV range on a trip you will also decrease gas use.
There are some circumstances where lower gas MPGcs will actually lower trip fuel consumption by allowing more EV operation.
Good Luck,
The volt is a fun car for a hypermiler