I tried losing my virginity but my boyfriend said my vagina is ‘too tight’ and he’s penis wouldn’t fit in without causing us both pain? Please help.

May be worth visit. If you are considering this step it may be time for you to see an OBGYN & have a basic evaluation. This would include education about birth control & STD's . That evaluation might find that you have a very thick hymen (uncommon) that would benefit from a simple opening procedure. Either way you can approach this part of your life with a better understanding of your body & risks involved.
You will have pain. Although you chose to pursue this action, your body is telling you differently. Perhaps you nor your body is ready for this huge decision and action. Listen to your body. It's okay to delay this action. Your boyfriend dhould accept your decision. Sexual intercourse at any age brings along its own set of emotional and physical baggage ( self-doubt, risk of STD's). Listen to your body. It's ok. .
Wait. Congratulations on your relationship. I agree with my colleague that your body is telling BOTH of you that it's not time yet. Focus on building what you have, and especially, explore other ways to enjoy one another's bodies -- these can be as satisfying or more satisfying than actual intercourse. You'll be glad you waited. Best wishes.