Tiimer problem

Unity Engine
1

Hey guys i have a timer running and as simple as it may seem i cant seem to add to it with breaking the structure. i want to add to once certain score markers are hit

here is the code:

public float Seconds = 30;
    public float Minutes = 0;
    public AudioClip mark;
    public AudioClip TimeB;
    
    
    // Use this for initialization
    void Start () {
        
        GameObject.Find("Timer").guiText.material.color = Color.white;
    
    }
    
    void OnGUI()
    {
        if (Seconds <= 10)
        {
            GameObject.Find("Timer").guiText.material.color = Color.red;
            audio.PlayOneShot(mark);
        }
        
    }
    
    // Update is called once per frame
    void Update () 
    {
        if ( Seconds <= 0)
        {
            Seconds = 30;
            if(Minutes >= 1)
            {
                Minutes --;
            }
            else
            {
                Minutes = 0;
                Seconds = 0;
                //This makes the guitext show the time as X:XX ToString ("f0") formats it so there is no decimal
                GameObject.Find("Timer").guiText.text = Minutes.ToString("f0") + ":0" + Seconds.ToString("f0");
            }
        }
        else
        {
            Seconds -= Time.deltaTime;
        }
        //these lines will make sure the time is shown as x:xx and not x:xxx.xxxxx
        if(Mathf.Round(Seconds) <= 9)
        {
            GameObject.Find("Timer").guiText.text = Minutes.ToString("f0") + ":0" + Seconds.ToString("f0");
        }
        else
        {
            GameObject.Find("Timer").guiText.text = Minutes.ToString("f0") + ":" + Seconds.ToString("f0");
        }
        
        if(Seconds <= 0)
        {
            if(Scoring.Score >= PlayerPrefs.GetInt("NewHighScore"))
        {
            PlayerPrefs.SetInt("NewHighScore", Scoring.Score);
        }
            Application.LoadLevel("Complete");
        }

sample of what im trying to do

if(scoring.score == 2500)
{
   timer += 15;
}

when i try this is break structure(meaning all of a sudden decimals are showing and it starts counting upward)

2

It’s working off seconds so:

if(scoring.score == 2500){
Seconds += 15;
}
3