God was not caught off guard by your failures. He was not surprised when you passed up the opportunity given. Unlike failing on a human, God already knew the decision you would make long before giving you the choice. Knowing your every sin you would ever commit against Him, He still chose to call you.

In fact, you gave Him an opportunity to lavish more Grace on you as He so desires too.

And therefore the Lord [earnestly] waits [expecting, looking, and longing] to be gracious to you; and therefore He lifts Himself up, that He may have mercy on you and show loving-kindness to you. For the Lord is a God of justice. Blessed (happy, fortunate, to be envied) are all those who [earnestly] wait for Him, who expect and look and long for Him [for His victory, His favor, His love, His peace, His joy, and His matchless, unbroken companionship]! - (Isa. 30:18 [Amplified])

Almost a scary thought (especially to a legalist) to think that if you sin you are providing God an opportunity to provide you more grace (and He does!), But let's listen to Paul.

What shall we say then? Are we to continue in sin so that grace may increase? May it never be! How shall we who died to sin still live in it? (Rom. 6:1,2, cf Romans 3:8)

When we sin, God's grace abounds all the more. We can't out sin God's grace no matter how hard we try, He wont allow it. If the cause of your sinning includes the reason: to give God opportunity to give grace, then Paul invites you to re-examine yourself, "...how shall we who died to sin still live in it?" (see Romans chapter 6 for further)

Maybe the speech the prodigal son prepared is similar to yours. After turning away from his father and squandering his inheritance on loose living, thus living an impoverished life as hired help envying the food he was hired to feed the pigs with; he begins thinking about the mercy plea he wishes to present to his father.

"But when he came to his senses, he said, 'How many of my father's hired men have more than enough bread, but I am dying here with hunger! 'I will get up and go to my father, and will say to him, "Father, I have sinned against heaven, and in your sight; I am no longer worthy to be called your son; make me as one of your hired men." (Luke 15:17-19)

God's response?

So he got up and came to his father. But while he was still a long way off, his father saw him and felt compassion for him, and ran and embraced him and kissed him. "And the son said to him, 'Father, I have sinned against heaven and in your sight; I am no longer worthy to be called your son.' "But the father said to his slaves, 'Quickly bring out the best robe and put it on him, and put a ring on his hand and sandals on his feet; and bring the fattened calf, kill it, and let us eat and celebrate; (Luke 15:20-23)

Notice the son was spotted "a long way off" and I bet what happened next was a huge surprise as it may be to you. His father "ran and embraced him and kissed him". I'd love to see the prodigal's face right now. His expectations of the fathers response was much different than the one he actually got.

He didn't even get to finish his speech, in fact, God didn't even give heed to what he had to say, after he got done kissing him and embracing him, He abruptly cut-off his son halfway through the son's speech, shouting bring out the best robe and put it on him, let us feast and celebrate!

Is your mindset like the prodigal's? Do you think of God as being discouraged, disappointed, or even disgusted with you? He's not. And the longer you wait to return to Him, the longer He will be looking for you, waiting passionately for your return.