It is not possible to resize a gadget out of the box on the dashboard, the sizing is hardcoded and set when the gadget is developed so to make any changes would require creating a new custom gadget based on the code of the original.
For more details check documentarian on Creating a custom Gadget XML Specification HERE
To locate the original gadget, to start out download the jira source code, and the gadget data can be located at - <your_atlassian_jira_src_directory>/jira-project/jira-components/jira-plugins/jira-gadgets-plugin
Catch up with Atlassian Product Managers in our 2020 Demo Den round-up! From Advanced Roadmaps to Code in Jira to Next-Gen Workflows, check out the videos below to help up-level your work in the new ...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events