Greetings
Don't worry, this is a regular retainer protocol followed post orthodontic treatment.
Your concern would be perfectly fitting if the retainers given were other way around, but ur lower teeth rest on ur upper teeth this situation (friction btw the 2 retainers) won't arise.
Please do wear ur retainer for the prescribed time religiously.
Next Steps
Visit ur orthodontist if the permanent retainer comes off and get it replaced immediately