It is maybe because of model parameters.
def count_parameters(model):
    params = [p.numel() for p in model.parameters() if p.requires_grad]
    for item in params:
        print(f'{item:>6}')
    print(f'______\n{sum(params):>6}')

count_parameters(model)


162
6
540
10
1170
13
17472
84
840
10
20
2
–
20329


20000 parameters might be very low for this Task.
I think i just need to raise these parameters.
Thanks for your Reply.