Hi Monviso
Lots of good advice here already, but I'll add a few things that may be relevant.
Obviously it's all down to practise, and unless you are very unlucky (and have no time sense at all) you'll improve as you practise more.
Like Bellyman I play in various bands and when I started classical lessons again 18 months ago, my teacher immediately pointed out that I tapped my left foot to keep time. I've had to make a conscious effort to stop that, which is really difficult as I'd been doing it for 45 years or so! But that experience of playing with a rhythm section has helped my sense of time a lot.
There are arguments for and against using a metronome. You don't want to sound metronomic. My teacher told me last year not to over practise with the metronome for that very reason. I generally use the metronome to check that I'm starting at about the right tempo, but rarely use it all the way through a piece, as most of the pieces I'm studying for ABRSM grade 8 have rallentando/ritardando/a tempo markings.
Perhaps try practising smaller sections of the piece(s) with the metronome periodically, rather than the whole piece.
We are always our own worst critics, so I suspect that your "more than sloppy" isn't as bad as your post implies.
Cheers
Simon
All round average Jazz, Blues & Rock player.
Currently working towards ABRSM grade 8.