Just relax...there is always something to worry about. Of course, this is coming from someone who is always worrying about something. Sometimes it is school, but often it is another issue.
I understand your concerns and others have given some great advice. However, remind yourself that if things aren't worked out right now, the kid won't be ruined for life. While it is not so great for the kid to be in a poor academic fit, for most, these kids won't be destroyed by the experience - they typically bounce back once they are in the right place. (Of course, a different topic would be why anyone expects elementary school to be challenging - the majority of kids in our district could easily skip a year or two of elementary with no harm.)
When my youngest was little, she had a medical issue which occupied me for the first few years. She still could benefit from another surgery, but she is now wary of being "put under", and the condition is such that the surgery is not a must. I still worry about how she will feel about her appearance as she gets older (she is 10).
This summer, we had our yearly school schedule conflict for my middle kid, who is going into 11th grade. We resolved it, but as always, she didn't get the level class she really wanted (last year she had to drop a level in a class; this year she skipped a level of another subject).
Then, middle kid realized she would need to switch travel ball teams. She just wasn't getting the playing time, so off to tryouts (which she hadn't done for a few years, since she had been with the team for a few years). Went to a tryout, got an offer, accepted, things looked good. Then a week later, the coach said he couldn't find players for a couple of positions and disbanded the team. Back to tryouts (many of which were now over) and received an offer from another team. So while it is okay now, there were a few stressful weeks.
I guess my point is that there is always something to worry about. Usually it works out in the end, but when you cannot yet see the end, it is difficult. Try to relax and good luck.