You are just 20. No one expects a maturity and compose in you like a sixty year old person. You are now in the transformation stage. Physical energy is high. Expectation from you is more than what it was a few years ago. But you are not fully equipped to cope up to that. That is why the confusion and resentment and the anger.
Anger, especially blurting out or blowing fuse is a sign of helplessness or deep confusion inside you. Many people of you age have that, but in varying degrees. But as you are conscious of it and want to curtail the short temper, it is welcome and you can achieve it if you try sincerely.
1. Do not become over self conscious. People are not much worried about you. The have their own matters.
2. Do not take things as too personal. Even if someone blames you, finds fault with you, tries to correct you, gives you some task to finish and point out your shortcomings, don't take it too personal. All of us are made what we are, by society. We grow, develop, improve only when someone tells us our faults, mistakes, deficiencies etc. So welcome or at least listen patiently thanking them to have given you opportunity to correct yourself at the earliest.
3. Do not react to anything instantaneously. Life is not 'fast finger forward first' event. When you press the anger button fast, actually it signals that you are pressing your panic button. The other side immediately sees your weakness and exploit it. Do not succumb to that. How? Before reacting take a little time to think all sides of the matter. Then reply or respond with civil and polite words.
4.Do not expect to win always. Accept defeat with grace. Take it with sportsman spirit. Do not throw tantrums.
5. If you have to differ, differ with proper decent words. Do not attack personally ; do not be abusive.
6. Remeber, anger begets more anger. Use a smile. when you feel angry. See the magic.
7. If you are a person in the habit of taking lot of spice, chillies etc then reduce that.
8. Mix and interact with more and more people- elder in age, more mature and experienced.
9. Take up a regular physical exercise like running, jogging, games etc.
10. Mingle and play with little children. Watch the team spirit and sportsmanship fro them.
11. Spend some time in calm prayers or meditation or sit in silence for some time everyday.
12. Do not overwork.Give yourself proper rest and entertainment also.
After all this, your anger is gone!