In my Father's house are many mansions; if it were not so, I would have told you. I go to prepare a place for you. And if I go and prepare a place for you, I will come again and receive you to Myself; that where I am, there you may be also." (John 14:2-3)
If you have trusted in Christ alone, you can be certain of your salvation. We'll keep this one simple and let the words of Jesus do the talking: "...if it were not so, I would not have told you."