I know, after all that effort, you're going to be itching to see it transition. It's a long and painful road to tune your multicopter mode before even thinking of transitioning.
Make sure you adjust all of the Q tuning parameters so that the multicopter mode is flying as stable as possible before doing any hybrid flights. You'll save yourself a lot of expense and headache.
When attempting transitions, make sure you are well above a minimum height of 20 m above ground level (AGL). Until you get all of your Q transition parameters set, you are very likely to lose altitude, or even lose stability on your first tests. Even then, stay above 20 m AGL.