Hi there. If your laptop’s i3 processor is a 10th or 11th generation (and you’re using its integrated graphics), there’s bad news. There’s been an issue with the game crashing sporadically on those processors for several months and Zwift will only say “we’re working on it, use something else”. The current thread can be found here: Intel integrated graphics gen 10 and 11
You should be able to recover the incomplete .fit file from Documents\Zwift\Activities but there’s no way to upload it back into Zwift.