I ABSOLUTELY disagree with you that this is a mortal sin. To be a mortal sin, an act must be a grave matter. It must be seriously wrong. Damaging a kitchen cabinet or similar item in these circumstances does not qualify, especially if the sinner did not mean any permanent harm at the time, and is willing to do the repairs.
I am sorry to hear the original poster say he(?) has problems with scrupulosity and is constantly worried about mortal sins. Please, be assured of God’s mercy! You cannot commit a mortal sin by accident! For a sin to be mortal, three conditions must be true:
- It must be a grave (serious) matter.
- The person must be aware that it is a grave matter.
- The person must give full consent.
Because of #2, you can NEVER commit a mortal sin and not know it.
Damage caused in an angry outburst might be a mortal sin if, say, you angrily and intentionally crashed into another car while driving, or struck a person weaker than yourself, or intentionally destroyed a very valuable object like a work of art. But not damaging furniture, which can be repaired.
Let me say it again: Please be assured of God’s mercy. Pray to God for help with your anxieties. Remember this prayer to Jesus from the Mass: “Keep us from sin and protect us from all anxieties.” If you pray this prayer regularly, then I am sure that Jesus will not let you fall into mortal sin without you first CONSCIOUSLY and INTENTIONALLY deciding to reject Him.