There are probably people who can run such an 800 but they are 5000m runners with lots of endurance and not much basic speed, not 800m specialists.
As others have said, 63 is more 2:20 or slower, unless one has very good endurance. I ran something like 59 and 2:15 in 9th grade which fits with what others have written.
If the pacer goes through around 50.0 (which is very fast, even for professional races) most of the athletes will be more at 51 and they will have 47-48 400m times. Unless one can run 1:43 50-51 is usually too fast and not an ideal split. There are other reasons why first laps are often so fast, it's mostly because the first 150-200m are run very fast, also for positioning.
I think this all is besides the point as we don't know enough about the poster. Running 2:16 with only 63 400 PB is something I'd expect from a female 5000m runner, i.e. huge endurance but quite slow. Most teenagers running track are not like that
Actually the calculation given is pretty good for my 400 pr and 800 pr lap splits. One thing that you should keep in mind is that your 400 pr might or might not be can accurate indicator of your 400 ability, maybe 63s was a really good effort for you and it'll be impossible to match the calculation in the 800, maybe you have 61s in you. If that 63 was a really good race, I'd add 4s lap 1 (67s) and 8s lap 2 (71s), to get 2:18 on an 800 run very well. But the 800 is very hard, and it'll probably take a couple races to get the experience needed to run the time you're physically capable of. This is true whether you've never run the 800 before or if it's rust buster season.
Also if you're younger than 14 or maybe 15, your 800 will probably be slightly slower just cause your body hasn't grown into it's high-effort endurance capabilities.
As others have pointed out, anything between 2:15 and 2:45, depending on your age and training.
As an example, my son is in 9th grade and is fit but not a runner. Sometimes he likes time-trialing on the track for fun and one day we raced a 200 where he run a 28-29. The next week we raced a 400 where he sat and kick on me and clocked a 1:04. Finally, we raced an 800 and he bonked badly at 600m while running 2:30 pace.
If you are young an untrained >2:30, if you have some training, between 2:20 and 2:30, if you are well-trained and have some endurance, you may break 2:20.