hmmm . . . a little confused by your explanation of what is happening.

But the back base should be helping you up. I would be more concerned if you did not notice that they were there.

Yes, the back spotter should be lifting and throwing to help as long as she is not directly underneath the stunt, isn't lifting you out of the bases hands, and isn't pushing forward.
For something at a prep level, you should actually be lifted a bit higher first (i've heard that the bases noses are a good reference) by all people on the ground and then "settle" into their chests. This is to create smoothness and eliminate an abrupt stop as the bases reach prep level.

chelsea is right...as long as the back isn't causing you to 'toe' the stunt, then
she's doing her job...

if the back is putting too much forward pressure on you vs. lifting, then this would be a safety issue...

Yeah the backspot is supposed to help the bases but if it's affecting your flying tell her to tone it down a little

The back spot should throw you. If that is necessary in the stunt but if the back spot is pushing you forward or out of the bases hands and that is not supposed to happen then tell your backspot to stop throwing so hard. A backspot on my squad lifted the flyer out of the bases hands and forward (out of the bases hands) I was the front spot, and this kept happening when we practiced. We repeatedly told her not to do that and at the game the backspot did it again and the flyer almost fell but even though the build didn't look right the flyer didn't fall and I had to tell the bases what to do
because I was the only one that knew to finish the
build off strong (I was the only girl who had cheered 2
seasons before that). Even though me, the bases and
the flyer knew what happened the backspot acted
like nothing went wrong so if it becomes a major issue
and your coach doesn't notice it maybe have the person only throw a little bit. The whole point of me telling you that was because sometimes people wont listen. My coach even told the backspot not to throw so much, but the backspot still didn't listen and someone almost got hurt.