Firstly, the norm is you spend say 5 minutes in prayer beforehand, to search your soul for sin, but since you are new to this and have a good span of time, I do not know. Perhaps 10 minutes? The main thing you do is go in there sorry for all of them, with the determination not to do them again. Don’t beat yourself over the head if you end up forgetting something. the idea is that you would had confessed it if you had remembered, because the emphasis is on that you wished to be wiped clean of all your sins in the first place. the bare minimum is that you confess ALL mortal sins you can remember at that time.
When you have recalled something you have forgotten later on, should you remember, mention that sin at the point of your next regular confession. You are free to receive Communion inbetween confessions like that, just as long as some instance of newly committed mortal sin hasn’t cropped up. Should that happen, you would discontinue Communions until receiving Absolution for the sins forgot the previous time and the current mortal sins at the next confession.
You have nothing to worry about, and at least you know your priest easily. You don’t have to confess face-to-face either, He needn’t know who you are. Even if he does know you, from what I understand from an EWTN priest, he hears so many confessions he couldn’t possibly keep track of them, and he also thinks that in his own case he is blessed with a Holy Forgetfulness in such matters. Whether all priests have that or not I do not know, but being behind a screen of some sort can make that pretty absolute.
