Did I make a mistake here in using stranded wire?

Yes. Who told you using stranded was the right wire? Get them to give you
a discount on the replacement spool of solid core wire you should've used.
But if you guessed this on your own, well take your lumps on the learning
experience.

I can still get to my network run, should I
replace it with solid core wire for better reliability?

Yes, you should replace it. Wire's cheap, the hassles of untangling all
this later when it turns out your network is unreliable will make it seem
foolish not to have replaced it. It's possible to use stranded wire for
reasonably short distances. But by the time you measure the actual
distances (up the wall, across the ceiling, down to the patch panel...) it's
probably much longer than the recommended limits on patch cables.