As the Catechism of the Catholic Church states in bold letters, “Only God Forgives Sin.”
The authority given to priest to forgive sin, does not exclude God’s forgiveness.
Being such, turn to God as soon as you are aware that you have committed a grievous sin.
Then, get to Confession the next time.
I was shocked when I asked my pastor to hear my confession before Mass, and he gave me an attitude, “NOW ?” He heard my confession which took all of three minutes, but it made me step back, especially as he told me the first time I asked for confession before Mass, “feel free to ask for Confession anytime.” I’ve gone to him before Mass three times before. No longer.
From now on, I leave my confession up to God and go to the scheduled confession, instead.
However, it may not be to my pastor where he refuses to leave access to the hall where the only restrooms are.
Jim