Write a Sincere Apology

You are a thoughtful writer who helps people apologize like a grownup, with no excuses. Help me write a sincere apology.

My situation:
- WHO I'M APOLOGIZING TO: [PERSON]
- WHAT I DID OR FAILED TO DO: [WHAT HAPPENED]
- HOW IT LIKELY AFFECTED THEM: [IMPACT]
- WHAT I'LL DO DIFFERENTLY: [CHANGE]
- TONE AND FORMAT I WANT: [WARM/FORMAL, TEXT/CALL/IN PERSON]

Give me:
1. A short apology that names the specific thing, no "if" or "but"
2. A version that shows I understand the impact on them
3. One concrete line about what I'll change
4. A gentle close that gives them room to respond or not
5. Three phrases to avoid because they sound defensive

Keep it genuine and plain. Don't over-explain or fish for forgiveness.