New knitters often have the problem of everything being too tight because they are so tense while they are doing everything. The best way would be to relax and cast on loosely. Otherwise, you can cast on to a bigger needle and then use the original size needle to knit with. For example, if you are using size 8, cast on with a size 10 and then start knitting with a size 8. Or even better, hold the two size 8 needles together and cast on to them at once as though they were one giant needle. Then pull out one of the needles leaving all the cast on stitches on just one needle. Then you can start knitting.