Hi oki,
I'm sorry that you've had such a painful and frustrating experience!
The vaginal canal is a muscle which can naturally change shape and stretch to accommodate objects like fingers, toys or a penis. If you're feeling "tight" that's most often because you're not relaxed or turned on enough just yet. Being that kind of excited + nervous that can come when trying to something new with a partner isn't always the easiest way to get fully relaxed and turned on! How about when you masturbate? Do you know how you feel and how your genitals change as you get more relaxed and into it? Have you ever used your own fingers or toys internally when you're alone?
Pain is your body telling you to stop, so don't push through it! This article gives a lot more info on painful intercourse:
From OW! to WOW! Demystifying Painful Intercourse. In short, take your time, like really take your time and have plenty of good water-based lube on hand. If you're still having trouble, it's worth speaking to a doctor.