I think these feelings aren't uncommon - at least in those struggling with severe mental illness. I struggle with this thinking too, especially deciding what to take in college soon enough.

What helps me is taking things one day at a time - not worrying about the past or the future, just what is going on NOW. It's definitely hard sometimes, but it beats wasting time and energy on what could happen.

If you find this problem is really affecting you negatively, perhaps you could discuss it with your therapist or psych, or even a family member or friend you're close to? Sending good vibes your way!