Hi everyone! I am new to knitting. I have learned several different cast on methods but only one that really works for me. I know how to do a knit stitch but for some reason I keep getting an extra stitch with every row that I add so my scarf keeps getting wider and wider. Is there anything special I should be doing at the end of the row to stop this?
Yes. You may be taking the yarn to the back of the needle over the top which lifts the end stitch and the 2 legs of it look like 2 separate stitches and you’re knitting both of them. When you turn your work, hold the yarn out to the side so you can see just the one leg of the first stitch.
It’s usually the first stitch of a row where you mess up like Suzeeq said, not the last stitch in the row. So that is where you need to be careful.
I checked that and I am doing that right…I just can’t figure it out. 
Are you waping the yarn over the needle? If you are, you are making a yarnover that becomes a stitch on the next row leaving a small hole called an eyelet for the stitch name.
What do you mean wrapping the yarn? Like, taking the tail of yarn that comes up from the ball, wrapping it around the right needle, pulling the loop through and then taking the loop off the left needle just like a regular knit stitch? If so then yes, I thought that was how it’s done…
She meant wrapping the yarn around the needle before you have it inserted into a stitch. Or between stitches or something.
No I have not been doing that. I thought I was doing well this morning but I started with 22 stitches and after a few rows I had 26…I am gonna give up soon!
Can you take a picture so we might be able to look and see if what you’re doing is clearly visible? That might help us figure out what’s happening.
If you are gaining one stitch each row, my guess is that it might be happening at the beginning of each row. When I first started knitting, working only in the knit stitch, as I got to the end of the row and turned my work, my yarn would inadvertently end up going over the needle, and the last stitch on the previous row would look like two stitches when the yarn was going back over the needle instead of staying in front of the needle. This made me ‘see’ two stitches, and then I knit both of them… so annoying… I don’t know that this is what is causing your scarf increase, but I can admit that I did that for awhile before I figured out what I was doing with my yarn…
Since you are making a scarf, you probably don’t have too many stitches to start with. One approach would be to place a marker every 3, 4 or 5 stitches, across the row… just so that you know exactly how many stitches are supposed to between each marker. Then when you do the next row, you will be able to identify [I]exactly[/I] where you are picking up the extra stitch, because you will have one extra stitch between the two markers where you are getting the extra stitch. If you can isolate where it is happening, that could help identify where; and a picture would help too. Don’t give up! 
We’ll get to the bottom of it!
KnitTogether’s advice is excellent, and such a good idea. I was going to suggest you work with only 10 stitches or less and count after each row and see if you can catch yourself. If you don’t get the mistake after a number of inches, maybe you’d be ready to tackle the scarf again. But what KT says is way better. You would be able to pin point where you are picking up the stitches and that will really help you solve the problem. Don’t give up too easily. Tapered scarves are nice too.