The samples in your song attack late.
I can tell you're using FL Studio.
So, to fix the attack,
1. click on your sample/channel. You should now have your channel settings menu up.
2. find the "INS" button and click it.
3. Click the red button next to where it says "time" and make sure the light comes on.
4. Play around with the "att" knob.
You've fixed it! :)