Just one step along a long path.........
Several good suggestions have already been made. I especially like Newgen Jock’s proposition that you fly in the jump seat as an observer. Not having the pressure to perform will allow you to absorb much valuable information.
One of the struggles with the initial check out is the sheer volume of material that must be mastered; new airplane, new company and a new job are a daunting task. This is compounded by your apparently limited previous experience (through no fault of your own).
Hopefully the company will decide to continue investing in you. Try to be confident and upbeat, thank them for the training you have already received, listen very carefully to everything they say. I would strongly recommend that you not be defensive or argumentative. When the time comes you may suggest a series of observation flights. The instructor and/or check pilot can make or break the situation for you. Unfortunately some of the process is subjective. Years ago an acquaintance of mine was unmercifully shown the door at a regional airline. Today he is a successful pilot at a large international carrier. Most of us experience several hard experiences during the course of our careers.
In today’s economic climate carriers can afford to be extremely picky. Sometimes the criteria may not be objective but political. Over such things you have little if any control. All you can do is your best and seek to improve continually. For whatever reason if this flying job does not work out IT IS NOT THE END OF THE WORLD. Decades ago a colleague made a series of poor choices and likely ruined their aviation career. In desperation they ended their own life. I am not suggesting you are that distressed. I recommend that you keep this situation in perspective. Do the best you can let the chips fall where they may.