Yeah! (好啊!)Let's go see a baseball game!
真对不起，我另有安排。
Sorry, I'm tied up. *be tied up“受(时间的)约束”。
Sorry, I have plans.
Sorry, I'm busy. (对不起，我很忙。)
I'm sorry, but I have other plans.
实在对不起，恐怕不行。
I'm afraid I can't.
I'm sorry but I can't.
谢谢您的邀请，可是……
Thanks for asking, but……
Let's go out for a drink. (去喝一杯吧。)
Thanks for asking, but I already made plans. (谢谢你的邀请，可是我有别的安排。)
Thanks for the invitation, but…… (谢谢您的邀请，可是……)
另找时间可以吗?
How about a rain check? *rain check指“(比赛、活动等)因雨天改期再赛时作为入场券的原票票根”。由因雨天中止或延期比赛而发给观众“rain check”引申为被邀请者因故不能接受邀请，而邀请继续有效的意思，“以后方便的时间”、“下次还有机会”。
Let's do it another time. (再找时间吧。)
Could we plan it for another day? (能找其他时间吧?)
Some other time. (再找其他时间吧。)
我希望你能来。
I hope you can come.