I am almost completely done with my store and have added all the final things I need to launch and I already signed up for a shopify plan which states on April 26th. I want to launch my store officially tomorrow; however when I try to test the checkout button or customize checkout, it generates the same cart page or shows the page cannot be loaded. Please help!
Sorry you are facing this issue, it would be my pleasure to help you.
Welcome to the Shopify community! 
Thanks for your good question.
Please share your site URL,
I will check out the issue and provide you a solution here.
Hey @lunassentials ,
Welcome to the Shopify Community!
It’s exciting to hear that you are ready to launch your store, I’d be happy to help you finalize the last steps.
Without being able to see your store, it’s difficult for me to establish what is happening with your checkout. Would you mind sharing your website URL with me so I can take a closer look?
Look forward to hearing from you!