cough syrup is making me high, how to get rid of that side effect?

You definitely did not get high off up two teaspoons. At most that could only be 30mg of dextromethorphan, the active ingredient that gets you high. It takes at least usually 200mg for a LIGHT effect. If you think you're high, you're only experiencing a placebo effect. I'm not trying to put you down, it's how it is.

If you still insist you're high, get some cough drops.

Find out from one or more alternative medicine books what resolutions are available to actually "cure colds and coughs." The drug houses (pharmaceutical) places, want to get rich on the backs of the people they are supposed to serve. Try the alternative treatments which are geared toward the natural way of healing ailments of all sorts. Remember this, What shall we then say to these things? If God be for us, who can be against us? - Romans 8:31. The Lord daily loadeth us with benefits, even the God of our salvation. Selah. - Psalm 68:19. Pay attention to what God is telling you. Daily read Psalm 35 (Plead My Cause). Then ask God to take care of the known and the unknown and protect you. As long as you follow the Lord's Will, you will be protected. For peace of mind, quietly say "Peace Be To This House." - Luke 10:5. Then peace will be transcend every other occurrence around you. Peace and God Bless.

Don't take the medicine when you have to go to class. Try tea with honey when you cannot medicate. For now, have a cup of coffee.

ask your pharmacist to help you get a cough medicine that won't give you that effect.

Hurrah, that's what I was exploring for! Thanks op of this question.

stop doing that.