Dear John,

This is your scrupulosity acting up.  The fact that you euphemistically shaded the sin does not negate the Confession ("lustful" and "sexual" both insinuate the same fundamental matter).  Unless you deliberately withheld a sin altogether, you are fine.  You did not do that—God knows all the dirty details about the matter, and truly most priests don't need to hear all the nitty-gritty in every thought or action.  

If you said,

"I had adulterous thoughts and entertained them deliberately for a long time,"

or anything like that, the priest would know enough.  You wouldn't need to describe the details of what you imagined.  

• Do you see the difference in the basic framework?

If he were to need more detail to understand the nature of the sin, he would ask for more; keep in mind, the priest has heard it all, so he is happy to get the gist of it and move on.  God is pleased that you got yourself into the confessional and are doing the work to try to hand over the mess; He is a loving Father, and we need to remember that when we are wrestling with our shame, He only wants to build us up, not tear us down.  

Scrupulosity tends to have a negative effect, so always balance that with a good grasp of God's Mercy.

Peace,