Problem with 2D slopes and walls

I'm trying to create my first controller script, trying to mimic the tutorials, and I'm having an issue when trying to go down a slope. Instead of walking smoothly down the slope, my character will just throw himself forward and then fall again, like this

I tried to modify the properties of my rigidbody, gravity and movement parameters, but even if I minimize it, this behaviour still appears to some degree.

I also found that when I touch a wall (vertical collider) midair, my characters stops falling as long as I press de directional button towards it.

I'll leave here my control script. I don't know what other information might be useful.

 using UnityEngine;
 using System.Collections;
 
 public class moviment1: MonoBehaviour {
 
 
     public float maxSpeed = 10f;
     bool dreta = true;
     public float jumpForce = 1000f;
     bool firstJump = false;
     private Transform groundCheck;
     private bool grounded = false;
     float groundRadius = 0.29f;
     public LayerMask Terra;
 
 
     void Awake()
     {
         groundCheck = transform.Find("groundCheck"); 
     }
     
     void FixedUpdate() {
     
         grounded = Physics2D.OverlapCircle (groundCheck.position, groundRadius, Terra);
         
         if (grounded) {
             rigidbody2D.velocity = new Vector2(rigidbody2D.velocity.x, 0);
         } else {
             
         }
 
         float move = Input.GetAxis("Horizontal");
 
         if (move > 0 && !dreta)
             flip ();
         else if (move < 0 && dreta)
             flip ();
 
         rigidbody2D.velocity = new Vector2(move * maxSpeed, rigidbody2D.velocity.y);
 
         if (Input.GetButtonDown ("Jump") && !grounded && firstJump) {
             firstJump = false;
             rigidbody2D.velocity = new Vector2(rigidbody2D.velocity.x, 0);
             rigidbody2D.AddForce(new Vector2(0f, jumpForce));
         }
         
         if (Input.GetButtonDown ("Jump") && grounded) {
             firstJump = true;
             rigidbody2D.velocity = new Vector2(rigidbody2D.velocity.x, 0);
             rigidbody2D.AddForce(new Vector2(0f, jumpForce));
             
         }
     }
 
     void flip() {
         dreta = !dreta;
         Vector3 escala = transform.localScale; 
         escala.x = -escala.x;
         transform.localScale = escala;
     }
 }