Thank you for your query. I would like to assure you that there is no serious problem at all. What you have experienced is very common with persons having sex for the first time. Sometimes, even those experienced in having sex regularly may have similar situations.
Please remember that sex is a normal phenomenon like eating or sleeping. Just like a person may not sleep well (e.g. like on the first night on a new place)or have a good appetite everyday, sex is also variable form day to day and time to time. Sex may not be very satisfying if a person is tired or sleepy or anxious.
Moreover, in those having sex for the first time, performance
anxiety is very common, which may lead to situation like yours. Moreover, in the beginning, couples are not experienced or familiar with each other's bodies and are not able to stimulate each other adequately.
The trick is to relax, and focus on having a good time with each other sexually rather than on performing extremely well to impress the partner.
I would suggest you to try to engage in adequate foreplay first, stimulating each other sufficiently to excitement before attempting intercourse.
Please remember that the stereotyped depiction of sex as in movies and porns (just like action sequences in movies) are neither natural, nor required for a satisfying sexual life.
Hope I've been able to satisfy your query. If you have any further clarifications, please don't hesitate to ask me. Best of luck.
Dr. Sourav.