Just a memory that has popped into my brain and which may sound familiar, louby.
A few years ago, having not played my violin for ages, I had a go on a friend's (very nice!) violin. To my horror I found I could barely play in tune except purely by ear (some rather graceless sliding about on the strings), and felt as if I had entirely forgotten how to play the instrument.
I got my violin out more or less the moment I got home, and found I could play it with some degree of competence even after all that time. In the end, it was just more familiar to me (particularly with its rather idiosyncratic size, which is "wrong" for a full size fiddle) even though my friend's fiddle is worth about twice as much.
Basically, I was used to MY violin... I had owned it at that point for over a decade - and playing another one, no matter how nice, was simply weird, especially when I was so out of practice.
Once I got back into playing a bit I found I could adjust to other instruments a little better, though I was still far more comfy on mine.
But the thing is, the real reason wasn't the quality of the violin, but my familiarity with it. If I am honest, when I first got this violin aged 12 (almost 19 years ago - argh!), it felt pretty weird compared to my old violin, and it took me some time to adjust. But undoubtedly, it's a better violin, and when I got to know it, I was fine.
false harmonic makes a good point that a well set up violin, if you've been used to one that is badly set up! A couple of years back I had my nice familiar fiddle set up properly... and boy, did I struggle for a while! I was used to having to press the strings really hard with my LH fingers, used to a really high bridge and how that (adversely) affected my bowing. Once I'd adjusted, it was so much easier to play, but at the start it was like having a new instrument, and NOT in a fun way...
You'll get to know your new fiddle, and learn to play it well, in time. Don't worry about it