I've done that myself before too, and this is what I did to fix it...there may be a more technical way, but this fixed it for me.
in the box where you type your user name - click inside the box and a 'subbox' for want of a better description shows up with your user name in it - mouse over that user name till it is highlighted then press your delete
button on your keyboard while the name is highlighted
a box will pop up that says
"Windows has a password that's stored for this username. Do you want to delete the username and password"
Then type in the correct user name and password and your correct one will then be saved.
Hope this helps
Microsoft MVP - 2010, 2011, 2012, 2013, 2014, 2015