Margins bigger on right side

To see if it is the printer, create a new document. Add a light gray rectangle that covers the entire page, and see how it prints. Is it centered, or off-set to one side or another? If so, in addition to Jeff's suggestion, the printer may have centering controls.

If you are referring to printing on a desktop printer, you should make sure you choose Center in your print options under Setup, Page Position.

See screenshot.

The uneven margins are most likely your printer feeding the paper unevenly. We have had ours occasionally drift so much that there is no margin on one side, and a half-inch on the other (instead of the expected 1/4 inch of white all around).

You can check if your page margins are set equally by selecting the document page or master page that you want to check in the Pages Panel and going under the Layout Menu to Margins and Columns. There it will tell you how the margin guides are set up and you can change them there if you wish. However, this will not assure that the actual text frames that you are using are actually aligned to those margins. Click on your text frame and see if it is actually aligned to the margin guides. If the text frame is actually aligned but the text is not then check the paragraph format panel to see if there is any right or left indent added and also check in the Text Frames Options dialog (Command-B on a  Mac and Control-B on a PC) to see if any inset spacing has been set in the text frame. For a document that has only one page size and orientation Liquid Layout is not necessary and should be turned off. If you actually want the inner margins of a spread to be larger (to accommodate the gutter) then set up the job in Facing Pages and in the New Document Dialog choose a different value for inner and outer margins.