14 weeks pregnant had brown bleeding. Went to ER and heart beat is normal. Fingers crossed. Is it normal? Low lying placenta seen in ultrasound

Normal. Many ultrasounds at 14 weeks are low lying. What and see what 18 week ultrasound shows to determine if your placenta is in a problem presentation. In the meantime, you might avoid intercourse. Brown blood is old blood, so it's hard to say when this bleed actually was. Good luck and hope no more bleeding!
This early, a "low- lying placenta means that an edge of the placenta covered the internal os of the cervix. As everything grows, bleeding commonly occurs as that part of the placenta degenerates and no longer covers the internal os. It may actually become anterior or posterior. No longer a problem - no further bleeding from that cause can happen. You need not curtail vaginal intercourse.
Er visit. The er visit evaluated you and found a low lying placenta as the cause of the brown bleeding. You have been properly evaluated and this is quite common.