I experienced this same problem with my first cup of sencha. It is a Japanese tea, and the leaves are very small, so they infuse water more rapidly than other green teas. If you like, steep your tea for less time (I prefer about 2 minutes rather than the suggested 3 minutes), or use less than 1 tsp./cup of water. In my opinion, sencha is an acquired taste, as it is not quite as sweet as the other green teas; however, make slight adjustments to your liking, and if it doesn't work out, just try a different tea!
"If Christianity is wine and Islam coffee, Buddhism is most certainly tea." - Alan Watts