Need help with mistake: row ended too soon

I am a new knitter and was on a roll until I somehow mad a mistake near the end of a row. Should be 20 stitches but ended with a knot at 19 then 20 is loose and weird. How do I go back and correct? do not want to restart and would like help correcting the error. Please help!

Hi and welcome to Knitting Help.
It’s a little difficult to say without seeing it but end stitches can sometimes be loose, especially in the beginning. You can take out the last row one stitch at a time to undo the mistake. Learning to undo your knitting and fix mistakes is a good technique to have.