Close to closing 1st deal! Need help!

[Joe Threats]

Good Afternoon BP, 

I was able to get my first property under contract about 3 weeks ago. Since I've gotten lots of people inquiring bout the property. Well today an offer was made and the the buyer wants to close this week. :)

I'm slightly hesitant but here's why. After agreeing on the price the buyer said he would send of over the contract. Once I saw it, it read Purchase and Sales Agreement. I was thinking it should have been the purchase of contract agreement. So I made it clear with them that the house was currently under contract and was looking for cash buyer. They replied with "I am not the cash buyer  but I do have a cash buyer wanting to close and yes I know you have it under contract" 

I guess my question is should I sign the PSA they sent over to me? Is there anything I need to do to make sure I don't mess anything up on my end? Thanks in advance for any advice I receive!