First time sex, couldn't get hard enough

Sounds to me like your biggest issue is stres! Stress will kill an errection very quickly and so will nerves.
Maybe worth getting use to being naked in front of your girl friend and start by doing mutual masturbation, have her give you a hand job and blow job until you are able to climax with her and then work up to intercourse. Once you are ready to try intercouse have her agin masturbate you until you are well aroused and almost ready to shoot, then insert it into her see if you can stay hard and give a good creamy load. Relax and enjoy it.

Thoughtful mothers, when they begin to notice frequent erections in their boys, will begin a special nighttime ritual at least several times a week. At bedtime, the mom will give her son a very relaxing and thorough back rub which puts the boy in a very passive relaxed sleep, with many boys almost asleep at that point. The mom gently helps flip the boy into his back and proceeds to give a very soft and soothing massage to the boys neck and chest. This puts most boys into a quasi-sleep mode. At that point, the mom simply moves the massage lower on the boy’s body, including his boxer briefs. Many boys at this point aren’t mentally aware or register what’s going on. He won’t notice (or care) when her fingertips start to gently massage his boxer briefs. Won’t notice when his penis begins to lengthen and stiffen inside the briefs. But mom will. She will then begin to focus her massage on the material over the head of the boy’s penis, the most sensitive area of his young body. He will attain a full erection very rapidly. He won’t notice when her fingers then begin to massage the glans of his penis, below the head, nor that her other hand is gently massaging the fabric covering his testicles. At this point he is fully sexually aroused. The mom will soon feel the wetness through the fabric of his precum. At this point, the mom will stop and use her fingers to open the slit of the boxer briefs, allowing her son’s erection to naturally come out in the open air. Using her son’s own precum as a lubricant, she can gently massage his entire penis with her hand to bring him to a full and quick ejaculation in his sleep. Some mothers instead will simply lower their mouth onto the head of the penis and using a combination of sucking and licking the head, bring the boy to ejaculate directly into her mouth.