As the bike is fairly new the problem may have always there but you'd not noticed it, or it occurred at the same time as you changed the chainring.
I'll assume though, that everything was working before the change and all that you changed was the chainring, and made no other adjustment. One of the following could be the issue. Start at 1 as the most likely.
The chainring has been installed incorrectly. Check all bolts and spacers are set correctly and tightly. There is info in the comments on your question. If necessary remove the new chainring and refit the old one, check the spacing between the chainrings and that the shifting works correctly. Then refit the new one and compare the spacing.
The front derailleur needs adjustment. You said in the comments that the front derailleur changes from small chainring to large ok. It may need some adjustment to the lower limit screw to make it move down / inwards a little more to give a better change from large chainring to small. This page gives info on adjustment:
The less likely solutions:
The chainring is not compatible with your crank or chain, compare it with the chainring supplied with the bike.
Chain length. When you change from large chainring to small the amount of chain used will reduce. This slack is taken up by the rear derailleur. As you've put a larger small chainring on, the rear derailleur is taking up less slack, there's a very slim possibility this is affecting the change.
If you removed the crank arm to change the chainring, it's not attached as tightly as before.
Try 1 and 2 and see if they solve the problem. Steps 3, 4 and 5 are included for completeness.