I would ask your pilot manager for help, and ask if your examiner could be there too.
Make sure that they fuly understand that you want their help and are NOT going to argue with them about your Line check. Go in with the attitude of 'Can you please help me ? Where did I go wrong and what should I do now to get back on the horse ?' Even at 2,000 TT, you are relatively new and inexperienced, so be humble and accepting.
Possibly better to put this request in writing, so there is no misunderstanding and they realise that you want their help and guidance and are not questioning their assessment.
Your record will stand, but as long as you show that it was an unusual mistake and that you have worked hard to overcome it, it should not prejudice your future career. We learn from our mistakes, after all. I can think of a person who departed the runway during an engine failure and RTO in the Sim, but went on to become a Captain.
And keep going. I've never failed a check, but I have technically failed the first day of a two day recurrent Sim. All passed the next day and all good.
So, get back on the horse ! We all have bad days, but we just need to put those behind us and move on. You will not have failed the line check for the original mistake, but how you dealt with the situation having made that mistake,
PS, if your hands slip on Airbus thrust levers, have a think about how you are holding them and operating them. There should be no reason for your hands to slip unless you are aggressively slamming them back, or not holding them properly.
The thrust levers are simply gently pushed back to the idle gate as you flare, (then reversers lifted and pushed into the reverse gate if you are using reverse).