Discovery Flight today...unexpected results

Hang in there. With the reasoning you've described, you'll get through
it. Notice I didn't say you'll get -over- it, to wit:

I've been a "new" pilot three times over the years: the first time as a
student pilot in 1963, the 2nd time returning to flying in 1978 after an
8 year hiatus, and again in 2000 after an 18 year break.

I can clearly remember each time having experiences like you describe:
serious nervousness, lots of sweat, a "death grip" on the yoke, even
shaking knees as I applied rudder inputs during turning maneuvers.
These symptoms gradually abated as I gained familiarity with the
environment and confidence in my abilities to manage it.

Such experiences have occurred at other times: the the first solo flight
(and a few more), during the practical (flight) exam for the license,
checkin out in a new airplane, even when taking the biennial flight
review. Although I don't -welcome- those feelings, I credit them with
helping me to be a good pilot by reminding me that it is my skill and
knowledge that makes for safe flying. And when I'm back on the ground,
the accomplishments of the flight, even dealing with the nervousness,
contribute to the enjoyment and satisfaction gained from the experience.

Keep flying; your dreams will be realized.

george