God is disappointed whenever we sin, before or after baptism. But he promises forgiveness for our sins.
When we are baptised, our sins are “washed away” (Acts 2:38; 22:16; 1 Peter 3:21). So anything we have done before then is wiped clean and God no longer sees us as sinners, but as his children, faithfully trying to serve him.
Of course, we all continue to sin after baptism, but our sins continue to be covered by the death of Jesus. The apostle John was writing to baptized believers when he said
If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. (1 John 1:9)
My little children, I am writing these things to you so that you may not sin. But if anyone does sin, we have an advocate with the Father, Jesus Christ the righteous. He is the propitiation for our sins, and not for ours only but also for the sins of the whole world. (1 John 2:1-2)
There is therefore now no condemnation for those who are in Christ Jesus. (Rom 8:1)
It is important to remember to confess our sins, change our behaviour, and keep trying to live as Jesus wants us to.