Hi and welcome to KH. Congratulations on learning to knit! Increasing accidentally is a common problem and there are different ways it can happen. If you're changing between knits and purls it's easy to have the yarn go over the needle instead of between the needles and then it will get knitted on the next row and you've picked up an extra stitch. If you're not paying careful attention at the end of the row when you turn you can pick up an extra stitch there too either with a yarn over the needle or by knitting both legs of the last stitch. Count each row and try to see where you're getting new stitches added. You might want to read through FAQ...Mysterious extra stitches? Look Here!
We've all been there. A little practice and it will happen less often.