It's perfectly normal to include parts of yourself into your characters. Every writer does it, and there's nothing wrong with it at all. 

However, during a conversation with some authors recently, we were talking about writing sex scenes and how some writers find them difficult to write, especially if in first person. One of the most common reasons for that difficulty was authors saying they couldn't imagine themselves doing the things they were writing about. 

And that right there is the breakthrough. 

You are not your characters. 

Read that again. 

Even if elements of you are in your characters, their reactions might not be yours. Things they say or do likely wouldn't be things you would say or do. 

This is important to remember because what your characters do have to match how you've written them. 

If your character is always anxious in social situations, they are unlikely to suddenly be the life and soul of a party, even if you would be.

At a time you think you wouldn't be brave, your character might be because they have experienced things you haven't and are better equipped to handle them. 

When you look at this, it seems obvious. But it's surprising how many times you will find your characters behaving in a way that isn't fitting to the situations you created for them. This is never something to worry about during a first draft, but when you read your book back, make sure you take a moment to consider how THEY would respond based on their circumstances. 

You are not your characters. ;)