The sin I'm talking about today is not a really bad sin but it's something that's against God. I try not to go against it, but I kept failing. What do I do? I hope I don't get the wrong responses of evil or from those who think they're better than me. Thanks but I want help.

I confessed it to God and prayed but it doesn't seem to help. I feel guilty and punished.
First of all, make sure what you call sin against God, is actually said in Scripture to be sin against God. Remember, the devil also calls good, evil. He and men make up commandments, that only guilt trip the sheep.
That said, double heartedness is experienced at one time or another by all Christians, including Paul in Romans 7, but there is deliverance from walking after the flesh: By destroying the work of the devil within the mind and heart first.
We must fight the good fight spiritually within first, and we won't sin bodily. Simply put: when we resist the devil and dismiss his thoughts of temptation, we won't do them.
For though we walk in the flesh, we do not war after the flesh: (For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;
Casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ.
Having therefore these promises, dearly beloved, let us cleanse ourselves from all filthiness of the flesh and spirit, perfecting holiness in the fear of God.
Sinning with the flesh begins with lusting from the heart, which begins with receiving tempting thoughts to sin.
If we turn to God for His divine power, to resist the temptation of the devil
within our minds, and not receive lust
into our heart, then we shall not sin bodily. For where no lust for sin is, there will be no sinning by it.
But every man is tempted, when he is drawn away of his own lust, and enticed.
Our words and deeds follow our minds and hearts; therefore, if we spiritually cleanse our hearts and minds
with Jesus' help, then we will follow and walk after the Spirit, and not after the flesh.
Grace and peace be multiplied unto you through the knowledge of God, and of Jesus our Lord,
According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
The sons of God don't have to take any thoughts from the devil. He can send them, even as He did to Jesus, who also was tempted like all men, but like Jesus, we don't have to receive them into the heart and do them.
Like Abraham chasing away the fowls, that seek to eat up the pieces of our sacrifice to God, so can we quench every fiery dart of the devil by our faith of Abraham and love for Jesus.
Conclusion: We must always ask ourselves, do we love supping with Jesus within our hearts at all times, or do we also like to entertain the lust of the world now and then and do it?
Once we understand and begin that good spiritual fight within, we then become overcomers to endure all temptation, which gets easier and easier in time, even as we exercise our faith with Jesus more and more.
I was exactly as you, and I could be again if I let down my guard, but we don't have to live like that.
And above all else,
do not believe anyone to tell you that only the normal experience of all Christians in this life, as though it is not possible to walk as Jesus walked.
Furthermore then we beseech you, brethren, and exhort you by the Lord Jesus, that as ye have received of us how ye ought to walk and to please God, so ye would abound more and more.
He that saith he abideth in him ought himself also so to walk, even as he walked.