As a beginner, its actually very hard to control the shorter swing properly. It will take some time and practice for your muscles to be able to control the swing.

For now, focus on feeling like you are making the exact same swing as your normal swing but only shorter. Just remember though, if you shorten your backswing, so is the followthrough. Think of yourself as a clock. If your backswing goes to 9, then your followthrough finishes at 3. If backswing is at 10, then followthrough is at 2.

It will take time before you can hit the ball solidly.
This is what I usually teach my friends who just started golf (I do this to warm up as well):
1) Start of with smaller swings, holding the club shorter. Say from 8 to 2.
2) Once that is consistent, go to 9 to 3..and holding the club longer as you go.
3) Make sure that you minimize any sway or unnecessary movements. Try to hit the ball "crisp".

You should be hitting even better once you get to the full swing as your muscles has to be able to control the entire range of motion at each point and helps "muscle memory".