I think it sounds really good. Up until 50 seconds in, I feel it's perfection. At the 50 second mark and beyond, I think it starts to get a perhaps a little too slow paced. I know you are trying to build tension and that the piece isn't finished yet, but maybe if you trim that section in half (where the violin repeats a section to finish off with a cadence), it would improve the flow of your piece.
But really good job so far, I can't believe this is your first classical piece.