It's just a part of life. Sometimes when I' ve worked with women around this issue, I've given them homework where they've had to fail at least once a day at something. This helps them get used to the fear by facing it directly. So what if you plan a sacred date and you don't keep it, just schedule another one. So what if you mean to write in your journal but you put it off, set out to do it again.
Failure is just another opportunity to practice at succeeding.
Once again it's important to remember who's driving the bus. You'll need to set firm boundaries with your in-laws in order to honor your relationship. Stick to your line and don't make excuses or debate the issue. Frame it in love and set that boundary then make darn sure that you back up that boundary with action. If you say you can't see them on Friday night, don't give in, otherwise you send a message that your word is not law.