Take time to just strum the strings. With your left hand mute the strings, then strum the strings. You take time to work just on making chords right? Spend some time just working on strumming.
Say 4/4 timing for 10-20 bars.
Strike the strings with the same pressure the whole time. The longer you can do it the better. Start with 1/4 notes then 1/8 notes. Change the strum pattern and do it again.
Once you get that down start changing chords as you strum. Not playing songs just practice changing chords while you practice strumming. Your mind will start trusting your hands to change chords while you strum and you will stop worrying about it.