Make up your mind
Definition 1 of 1
Pro Tip 1/3Indecision
Use it when someone can't choose between options and needs a push to decide. 
If you keep hesitating, you'll miss the opportunity. Make up your mind!
Pro Tip 2/3Urgency
Implies a sense of urgency or frustration from the speaker towards the decision-maker. 
We don't have all day. Please make up your mind now.
Pro Tip 3/3Encouragement
Can be used to encourage someone who is afraid of making the wrong choice. 
Don't worry about making a mistake; just make up your mind and go for it.