No doubt!

Matthew 14:31 And immediately Jesus stretched out His hand and caught him, and said to him, “O you of little faith, why did you doubt?”

How do you know, that you know, that you really know you are saved? If you have repented of your sins, asked Christ for His forgiveness of them, and for Him to be the Lord of your life, you are now a child of His and eternally secure. Has your life changed as a result? Did you immediately return to sin or have the desire to change? That desire to change inside you is His Spirit that wants to live a life glorifying God, not in rebellion any longer. The doubt that you are feeling is from Satan. The more time you spend with God in prayer and His Word, the stronger your assurance is of your Salvation. If you continually seek God and the things of God, you will attain the peace of God and the assurance is a by-product. This assurance if a promise from God – Titus 1:2 in hope of eternal life which God, who cannot lie, promised before time began.

This below is from a resource at GotQuestions.org that was so good I had to include it here.

Question: “How can I have assurance of my salvation?”

Answer: How can you know for sure if you are saved? Consider 1 John 5:11-13: “And this is the testimony: God has given us eternal life, and this life is in his Son. He who has the Son has life; he who does not have the Son of God does not have life. I write these things to you who believe in the name of the Son of God so that you may know that you have eternal life.” Who is it that has the Son? It is those who have believed in Him and accepted Him (John 1:12). If you have Jesus, you have life. Not temporary life, but eternal.

God wants us to have assurance of our salvation. We cannot live our Christian lives wondering and worrying each day whether or not we are truly saved. That is why the Bible makes the plan of salvation so clear. Believe in Jesus Christ and you will be saved (John 3:16; Acts 16:31). Do you believe that Jesus is the Savior, that He died to pay the penalty for your sins (Romans 5:8; 2 Corinthians 5:21)? Are you trusting Him alone for salvation? If your answer is yes, you are saved! Assurance means “having been put beyond all doubt.” By taking God’s Word to heart, you can “put beyond all doubt” the fact and reality of your eternal salvation.

Jesus Himself affirms this regarding those who have believed in Him: “I give them eternal life, and they shall never perish; no one can snatch them out of my hand. My Father, who has given them to me, is greater than all; no one can snatch them out of my Father’s hand” (John 10:28-29). Eternal life is just that—eternal. There is no one, not even yourself, who can take Christ’s God-given gift of salvation away from you.

We hide God’s Word in our hearts so that we do not sin against Him (Psalm 119:11), and this includes the sin of doubt. Take joy in what God’s Word is saying to you, that instead of doubting we can live with confidence! We can have the assurance from Christ’s own Word that our salvation will never be in question. Our assurance is based on God’s love for us through Jesus Christ.