I am not convinced that your pcr product is specific. You have a large primer dimer and I think that the largest band may be non specific amplification.

Try a hot start reaction and run a temperature gradient taking your annealing temperature higher to see if the larger band persists or disappears as the Ta increases then interpretation of the gel may become simpler

For obtaining one band in 529 bp as product must be increase annealing temperature.

But can gave the details of your program.

You absolutely need to add positive and negative controls on your gels Without such PCR controls it is impossible to conclude anything from your gel.

Paul Rutland Can you be more explicit/clear. Non specific amplification

by non specific I mean that the largest band is not what you want amplified and may just be a sequence not related to the stronger ( and probably correct) amplimer of 529 bases and is just generated by one or both primers annealing in the wrong place but to a similar but not identical sequence. If this is the case then raising the annealing temperature or adding DMSO will probably cause it to disappear but if it is the longer allele of the repeat then it will remain for as long as the short sequence amplifies because then they will both anneal to the correct sequence outside of the repeat, An annealing temperature gradient will distinguish between these 2 situations

Paul Rutland I will do so and come back to you as soon as i am done. Thanks.