I'm not really good wioth this plane but I have seen a few do the same thing and it always seemd the rear "elevators" (v-tail had the trims set wrong) It could also be the way you are hand lauching it. You really do not throw it, you go to full throttle, point it into the wind and toss it gently at a very slight angle upwards, then quickly add up elevator to get the plane to climb. Be careful not to add to much "up" as this will cause the plane to quit flying (called a stall) then come rioght down into the ground

Also, see if there is a club close by, a lot of times most people will gladly help even non-members help to get a plane flying but some will not unless you join.