My object/group is not centered in the dotted lines outlining it. Can you help?

Therefore I cant get is parallel or aligned. It is on an angle. Rotate will not do it.
Thank you

Share the file so we can help you.

Are you using the free web version of SketchUp?

If the object is not centered in the dotted outline it means that there is probably some stray geometry far from it.

Try this in the context of the object:

1 - Select all.

2 - Press and hold down the Shift key to Add/Subtract from the selection.

3 - While stil pressing the Shift key, do a window select encompassing your object. This shall deselect it and any stray geometry shall remain selected.

4 - Press the Delete key. The stray geometry shall be deleted and the bounding box shall be close to the object.

Of course, if the stray geometry is in line with the object, it may stay in place. If this is the case, orbit the model by about 90° and repeat the procedure.

As pointed by Dave, posting the model would help a lot.