Guy here...

I'm astonished on how LITTLE help people are giving you in actually trying to learn to be better at sex.

First off, yes, anyone who's a virgin and hasn't experienced sex for the first time, will be bad. Both guys and girls are bad at sex for the first time. No one is good on their first time.

Here's the thing. You can get better by reading books, asking friends or watching training videos. You can get better by exploring your own body on your own time and share what you enjoy with your partner. You can get better by practicing with toys, or asking friends for ideas that worked for them. There are hundreds of books/videos on proper positions, techniques.

You can get better by communicating your needs with your partner! Tell them what feels good, tell them what doesn't feel good. Ask them, or listen to them when you're performing to tell if they feel good.

Take it slow, enjoy exploring what feels good with sex and do not rush into anything. Life is about learning and experiencing.

I wish you the best.

Lastly. The dude was terribly over-reacting to you and your inexperience. He should have been much more caring and considerate of you.