Thank you for the question.
The matter of concern is whether you deliberately withheld confessing sin, and I do not see that applies in this case.
While it is good and proper to specify number it is not necessary to always be absolute each time, provided you are not trying to deliberately conceal something. Most people have imperfect recollection and that does not change the validity of the sacrament.
You must learn to trust in God's Mercy and understand that He sees you trying to do right, and despite your flaws He loves you and is trying to raise you up, not put you down.
In a case where you later remember that you forgot something truly serious in a Confession, just bring it to the next Confession and say you forgot last time. God will not strike you down and send you to Hell in the meantime. God knows a contrite heart and always opts for Mercy whenever we turn to Him.
Keep in mind that the devil can use scrupulosity to try to defeat us and force us into despair. You must exercise greater trust in the Mercy of God and not let scrupulosity take root.