i dont believe in Allah is Merciful - that word is out of my dictionary
In which case you will never receive any mercy and you'll remain in a heedless and miserable anti-Allah state your entire life.
Allah will misguide you. You'll blame everything and anything that doesn't go your way on Allah. Who knows what state you would die in, if Allah continues to misguide you. Keep in mind that our absolute aim is to attain Jannah and avoid hellfire. If we die without iman, we have to face an eternity in hell. Just try to comprehend and reflect on that for a moment. No amount of emotional or physical pain we receive in this world would compare.
Why would Allah misguide you? Due to
your own attitude and approach. Allah is as
we think of him to be. If we think him to be unfair, then that is how he will treat us. If we have a positive and trusting, yearning, loving, patient approach to him then that is how he will be to us.
Have humility and sincerity in front of Allah. If you have comitted a sin, you should beg for forgiveness and don't assume you are entitled for anything.
If you want Allah's mercy, then beg for it whilst believing with full conviction that he will give it to you. In order for your dua to be accepted, you have to do what he asks of you and avoid sin/pray salah and do the obligatory to the best of your ability.
Total conviction and trust with a positive attitude to Allah is KEY.
Don't ask Allah bitterly. Don't pre-conclude the result of your dua to be negative.
Reflect over the fact that this life is temporary and fleeting. Be patient throughout the trials by resigning yourself into accepting that Allah is indeed All Wise and that whatever is happening to you is better for you ultimately in terms of deen, even if you can't see why at the time. Be thankful during the good times but don't be too happy as happiness is not everlasting.