I would suggest giving the Church a call and talk with a Priest. Also remember when you do make your first confession - you need to understand what confession is of course, examine your conscience and confess any and all mortal sins in number and kind (murder 3x, adultery 2x, missing mass -not sure how many times but only went a few x in the last 2 years (if one does not know the number for a mortal sin one can approximate according to what one knows…many times, few times, around 5x)).
Not sure what one would do in your situation. But certainly some instruction is in order and it can take a bit of time to make a first confession. But your Priest can guide you about going and then help you to -just tell him your situation.
Even if you could go as you ask – likely be best for you to go over privately for a meeting. A Penance service where there are lots of people may not be the best time to do such even if one can. Just give a call (but prepare first) and go see the Priest.
catholicnewsagency.com/resources/sacraments/reconciliation/
scborromeo.org/ccc/p2s2c2a4.htm (rather detailed from Catechism - it may be too detailed for you at the moment -but I do not know your background)
vatican.va/archive/compendium_ccc/documents/archive_2005_compendium-ccc_en.html
I am not discouraging you from confession of course! So give your Pastor a call he can guide you!
(tell him too about not yet receiving Holy Communion – one would need instruction etc)
In Jesus of Nazareth (and thus in his Sacraments) is true life!