Writing with my left hand, am I risking my chance of going to heaven?
Let me tell you straight away that no one will go to hell for using his left hand for eating, drinking, and writing or indeed for any other purpose. Any one who suggests otherwise does not know and makes a huge assumption, which he cannot substantiate. Indeed such a person betrays a degree of ignorance of God, His compassion and fairness.
What we have to remember is that God knows every aspect of a person’s abilities, motives and intentions. A left-handed person does not choose to make his right hand the weaker hand. This is something that he is created with and cannot change just like [he cannot change] the color of his [skin,] eyes or his hair.
So God will not ask anyone why he is left-handed, because it is He who has created him. Besides, using one’s right hand for eating and most other purposes is recommended, or a Sunnah. This means that it is not obligatory.
On the Day of Judgment, God will not ask any person why that person has not done something that is not obligatory. Nor will he punish anyone for not doing such a non-obligatory matter. He will look at what recommended practices we do in this life and reward us for them. But He will not punish us for omitting any of them.
In the question of which hand to use for eating, God will reward those of us using their right hands only if they choose to do so in response to the Prophet’s recommendations or to follow his example. In other words, His reward is not for the action itself but for intention behind the action. Hence, if a left-handed person trains himself patiently to eat and drink with his right hand until this becomes quite easy for him, and he does all that in order to follow the Prophet’s example, he is sure to earn more reward than a person who does the same but does not have the added difficulty of being left-handed.
I know some people who have done that. Their action is certainly commendable. The habit they acquired has become natural to them to the extent that they do practically everything with their left hands but when they eat they use their right hands. Perhaps you could do likewise and be patient until it comes naturally to you.
You only need to be patient with yourself. But if you find it too difficult, then you should not bother about what people may say. You just explain that this is a natural difficulty and that it is God who created you so.