scoring issues in pong

[metulburr]

You should read through my series of tutorials. You have bottlenecks (loading your images in the main game loop)

    win.blit(pygame.image.load('BG.png'),(0, 0))

and magic numbers all over the place.

#ball movement
 
    if x1 > 600:
        score1 += 1
        x1 = 305
        y1 = 245
        xvel *= -1
        yvel *= 1
 
         
 
    if x1 < 0:
        score2 += 1
        x1 = 305
        y1 = 245
        xvel *= -1
        yvel *= 1
         
     
    if y1 >= 490:
        yvel *= -1
 
    if y1 <= 10:
        yvel *= -1
 
#paddle collison
 
         
    if x1 >= 560 and (y1 < yp1 +65 and y1 > yp1):
        x1 == 559
        xvel *= -1
        yvel *= 1
 
 
    if x1 <= 25 and (y1 < yp2 +65 and y1 > yp2):
        x1 == 26
        xvel *= -1
        yvel *= 1

You are not using pygame rects for position and drawing at all making it spaghetti code. So its makes it more time consuming to follow flow, in which time i do not have.