ok so I have a 2D shape made from lines, I have a Vertex position color for each point on the shape, I want to rotate the shape, the problem is at the moment I am trying to rotate it using a rotation matrix but the thing just get stretched vertically, any help to how I can solve this?

The lines of code that rotate it are as so...

mOffsets[i].Position.X = (float)((Math.Cos(angle) * mOffsets[i].Position.X) + (-(Math.Sin(angle)) * mOffsets[i].Position.X));

mOffsets[i].Position.Y = (float)((Math.Sin(angle) * mOffsets[i].Position.Y) + (Math.Cos(angle) * mOffsets[i].Position.Y));

mOffsets is a VertexPositionColor array, I need to rotate these offsets around the origin...

Any help is appreciated.

Is this what you're looking for?

Matrix rotation = Matrix.CreateRotationZ(angle);

no thats not it, the problem is that the points I store are in VertexPositionColor format not in a matrix format so I cant perform matrix multiplication hence my messy peice of code wich is just mimicing a matrix multiplication, if this helps: the shape compresses in the following way: (not angles are in degrees, but are converted to radians in the actual program)

0 - 45 squashes the shape on the horizontal plane

45 - 90 uncompressesthe shape on the horizontal axis

80 - 135 compresses the shape on the vertical axis

135 - 180 uncompresses the shape on the horizontal axis the shape is now flipped upside down.

The multiplying your position through the rotation matrix suggested above will do this, but if you want to write it out your way, try: 

float newx =  (float)((Math.Cos(angle) * mOffsets[i].Position.X) + (-(Math.Sin(angle)) * mOffsets[i].Position.Y));

float newy =  (float)((Math.Sin(angle) * mOffsets[i].Position.X) + (Math.Cos(angle) * mOffsets[i].Position.Y));

mOffsets[i].Position.X = newx;

mOffsets[i].Position.Y = newy;

now I'm not sure what the coding difference is there but that fixed it,

ty :D

Just so you know, you can rotate individual points using Matrix rotations.

Your rotated X position depends on mOffsets[i].Position.X and mOffsets[i].Position.Y, instead of mOffsets[i].Position.X and mOffsets[i].Position.X. Likewise for the Y coordinate.