Entered data appears TWICE in table!!?

I'm JUST getting started with the online SQL tutorial at
http://sqlcourse.com. When I create a table and insert data, the data
appears TWICE. A simple example:

***Create the table:

create table rnmrgntable
(first varchar(20),
last varchar(30));

***Insert data:

insert into rnmrgntable
(first, last)
values ('Bill' , 'Smith');

***Then look at the table:

select * from rnmrgntable;

And I get:

first last
Bill Smith
Bill Smith

EVERYTHING I enter appears twice, duplicated on two rows as in this
example. What the heck's going on?

Ron M.