Run the Apple Diagnostics to see if any issues are detected.
Try unplugging the charger from the electrical outlet for a minute to reset the charger's circuitry. Also try using another known good electrical outlet especially on another electrical circuit.
Are you using the correct charger and charging cable?
Is the charger connected directly to the laptop? If you connect the charger to a multi-port adapter, dock, or hub, then the full power of the charger may not reach the laptop. Also try using the other USB-C port.
Have you used any third party chargers with this laptop?
Try disconnecting all external devices in case they are interfering.
Is the laptop being used heavily? If so, then all the power may be going to run the laptop instead of charging the battery. You can try stopping any CPU intensive workloads to see if the laptop charges faster. Completely power off (shutdown) the laptop and let it charge for at least 30 minutes or an hour. Power on the laptop to see how far the charging process has gotten. Did the battery charge a bit better/faster? The latter option can be a temporary solution until the laptop can be repaired if there is a hardware issue.
Here is an Apple article for troubleshooting USB-C charging issues:
https://support.apple.com/en-us/HT204652
You do have 14 days to return the laptop for any reason. Here is how you prepare a Mac if you are getting rid of it in order to remove your personal information and to disassociate your AppleID & accounts from the Mac:
https://support.apple.com/en-us/HT201065