I think you’ve accidentally knitted your purl row… or purled your knit row as @knitcindy said. If you were in the flow of knitting then came to the end of the row and turned and continued to knit instead of purling. Or vice versa.
It might not be the entire row.
Probably need to tink back several rows past the row in question and redo it.
As you tink (undoing each stitch and putting them on the needle, there are video tutorials if you need one) it isn’t too important to get the stitch mounted correctly every time as you are going to undo several rows, but on your final row check every stitch is mounted correctly before you start to knit, or purl, again.
Another option is to put in a life line below the incorrect row which allows you to pull out all the rows above but saves your stitches. It takes time to put in the life line and pick up the stitches but you might prefer it to tinking. After pulling out again you need to double check the mount before starting to work th stitches again.
Hope this helps