Retirement tax questions

Thank you.  My husband had no contributions in 2020 and I contributed $6500 in the Spring (at a low point in the market).  My understanding is that we can carry forward the excess contribution - the custodian of my IRA suggest I do so, since it has performed extremely well and would be subject to a 10% penalty if withdrawn.  This is assuming I would have enough earned income to carry it forward, so I suppose I will file for an extension in April if unsure.  Any thoughts on this?  I really appreciate the input.