Few of us are blessed with the ability to spell every word correctly every time. Fewer still can type 100% accurately.
Fortunately the spell checker is on hand to address the problem. Unfortunately, it's all too easy to forget to use it, and many spell checkers are set up incorrectly anyway.
Check that your spell checker is set to check in the correct language (many in the UK, for example, are set to US English) and get into the habit of engaging it whenever you write.
