Worst sex...how do I say it?

I started seeing this guy. Very sweet but our first time together was tough. I didn't feel a thing, he's small but I still gave it my all because sometimes it's not how large a guy is but his technique....he was very limited in his actions. He told me...because he was having difficulty, he appreciated my patience and gentleness...and honestly he was trying.

I left feeling nothing inside, actually left hornier than when I got there . He wants to get it on again...I'm worried it will get worst.

How do I tell him. I hate hurting anyone's feelings. I do enjoy his company. I think sexually we are not a good fit.

Advice? Thank u

UPDATE:

I let him go gently saying we aren't compatible...especially when he said he loved me, it was only 1 week knowing him. I had to block him because the msgs and phone calls were getting to be constant. Thanks for the advice.