I am a Green Card holder (CR1) who is a spouse of an American citizen. My Green Card will expire in March 2020 and I am planning to travel abroad from the USA in December and when I come back it will be in January, so is it okay to travel?
You are OK to travel, if you come back in January 2020 since your Green Card will expire in March of 2020 provided you have a valid travel document (passport or refugee travel document).
I assume your intention is to become a US citizen and therefore please note the following from FindLaw: Immigration
..to become a naturalized citizen ... you must have been physically present in the U.S. for at least 30 months out of the previous five years to establish continuous residency