It's possible. The pull out method is not a reliable form of birth control. Neither is taking a shower. Also, even with perfect use, the pill is not 100% effective, so pregnancy is always a possibility every time you have sex.
If you tend to be late with your pills a lot, then you should look into a backup method such as condoms or spermicide, or set an alarm to remind you to take your pill at the same time.
However, I would not panic about today unless you have been taking your pills more than six hours late or if you have been forgetting some days altogether. Just be careful in the future.