Okay, I've been flying electrics for 4 years and have around 20 E planes including all my glow planes. 1st.....make sure you got the prop on right....I had a sky scooter and it wouldn't fly worth crap. Found out I had prop on backwards. 2nd....the battery pack.
Probably nimh batts. That chemistry of batteries needs 5 to 7 full cycles (charge/discharge) before you reap the longetivity and power of the cells. 3rd, hand launch it into the wind! Give it a good straight out throw. As a reminder, fly right after you charge the batteries.
If they are a little warm off the charger and you put them in your plane, you shouldn't have much difficulty.

Dave...