OpenTK (C# OpenGL) Coordinate mistake

Question

I am trying to make a 2D renderer using OpenTK and I am having trouble with the coordinate system. I have followed an opengl sprite tutorial and the Size vector is defined by pixels, however the Position is behaving really weird, like it is already off the screen when Y = 5f

Here is my vertex shader

#version 330 core

layout (location = 0) in vec2 aPosition;
layout (location = 1) in vec2 aTexCoord;

out vec2 TexCoord;

uniform mat4 model;
uniform mat4 projection;

void main() {
    gl_Position = projection * model * vec4(aPosition, 0.0, 1.0);
    TexCoord = aTexCoord;
}

Here is my projection matrix (calculated in GameWindow.OnResize)

protected override void OnResize(ResizeEventArgs e) {
    base.OnResize(e);
        
    GL.Viewport(0, 0, e.Width, e.Height);
    ProjectionMatrix = Matrix4.CreateOrthographicOffCenter(0, e.Width, e.Height, 0, -1.0f, 1.0f);
}

And here is my model matrix calculation:

var model = Matrix4.CreateTranslation(Position.X, Position.Y, 0f) *
                Matrix4.CreateTranslation(0.5f * Size.X, 0.5f * Size.Y, 0f) *
                Matrix4.CreateRotationZ(MathHelper.DegreesToRadians(Rotation)) *
                Matrix4.CreateTranslation(-0.5f * Size.X, -0.5f * Size.Y, 0f) *
                Matrix4.CreateScale(Size.X, Size.Y, 1f);

shader.SetUniform("model", model);
shader.SetUniform("projection", Program.Window.ProjectionMatrix);

And finally, the SetUniform method on the Shader class

public void SetUniform(string name, Matrix4 data) {
    Bind();
    GL.UniformMatrix4(GL.GetUniformLocation(ID, name), false, ref data);
    Unbind();
}