A lot of earbuds don't fit that well, and this can be especially true if you have small ears. Earbuds like the classic white ones that come with the iPod are not very flexible, and will often incorrectly fit their owner. There is also risk from wearing earbuds that are too large because they can put pressure on the inner ear canal, causing pain during use. However, instead of suffering with this there are a couple of alternatives you can try.

More recent earbuds come with gel tips instead of the older showerhead style plastic ones. Just on their own, this style is a better as the tip of the earbud is more pliable. A lot of earbuds, like these Sonys come with detachable ear tips so you can use the smallest ones they come with. Also, if you want to avoid buying new earbuds, you can look if there are any replacement tips for the model you already own. There are many brand and off-brand options that you can look for at Amazon.

Another option is to buy child versions of earbuds like these Ultimate Ears. Since these are made for kids they are already a small size, so no switching of eartips necessary. However, one thing to be aware of is that they have a noise limiting feature to prevent to volume from going too loud. This could be something you may or may not prefer to have.

Finally you could try avoiding the standard in-ear earphones all together. An over-the-ear style model may be a good alternative. Since the earbuds are held in place with clips, you wont have to shove the earpiece as snugly in you ear which will allow some extra space.