Program won't let me open task manager or right click it.How can I close it?

So I'm playing a game called Terraria,and I got a rare item to summon a boss.Used it,couldn't beat the boss,and want to close the program to go back to my last save and try again.But it won't let me.Right clicking on it does nothing and alt tab del just beeps and does nothing.How can I close it without task manager or right clicking?