Firstly, as a first game this is really good! As far as execution is concerned it is amazing. It seemed like an interesting game mechanically. However, you've made a few mistakes that even I made before playtesting in my Pong style game.
So firstly, Players kept saying that the ball would shoot of before they were ready. To address that i made a countdown before the ball launches and then a .5s pause before it shoots off. You could also slow down time do something else to show that the ball is on the move now.
I too, have pickups. However my players didn't know what they all did so i decided to make a little popup saying like "ball speed up" or "paddle size increased" to make it super clear. (what are tht cheese and turtles for? are they good or bad?)
Another thing is a tutorial of some sort. In-game would be too much effort to expect in 3 days and even I just went with a static text box in-game but I think players would like your game more if you added at least a written explanation of your mechanic to your game page (again what do the cheese and turtle do?)