No, you'll just make a mess. :-) A toilet seat is not going to be covered with toxic substances that will collect in your own urine and bounce back up to you and hurt you. You're fine.
Next time, feel for the toilet seat with your foot and put it up, so if you miss, it won't make the seat wet that the next poor sucker might have to sit on.
I agree. Toilets are generally pretty dirty but you aren't going to give yourself an infection by your own urine splashing up on you from the toilet seat. Do you have a lot of anxiety in general?