There are two people in this world: Those who rush and send a message without thinking twice, and those who think about it endlessly, until they lose their temper and don't send it at all. For the former, WhatsApp has a solution!
If you've sent it and noticed a spelling mistake, regretting being a little more dramatic than you should be, we can tell you that Mark Zuckerberg has notified people on Facebook that you can now edit the sent messages and for them done, you have a full 15 minutes. Enough, right?
That is, if you write to the person you like: "I have you as a sister/brother" and he/she replies: "Me too", just edit it to "I love you very much". So simple. ;)