h264 bitrate exceed my value in runtime

[Amirhos-esm]

hello
I am using this Configuration for my encoder.

VencH264Param h264ParamDefualt = {
.bEntropyCodingCABAC = 1,
.nBitrate = 1 * 1024 * 1024,
.nFramerate = fps,
.nCodingMode = VENC_FRAME_CODING,
.nMaxKeyInterval = fps,
.sProfileLevel.nProfile = VENC_H264ProfileMain,
.sProfileLevel.nLevel = VENC_H264Level31,
.sQPRange.nMinqp = 10,
.sQPRange.nMaxqp = 32,
};

but I wondering why bitrate exceed 1 * 1024 * 1024