Travelling to Quesada

On the Costa Blanca Forum there was a post from a couple in a similar situation but they were already in France at the Spanish border when the lockdown began and had been refused entry on the main E15 but eventually got through at Port Bou. They were already on their way though and as other posters have said, it is better you stay where you are. If the completion date was 2nd April I can only assume you have somewhere to stay in the UK, so stay there.

Hi Steve and Jackie,
It's not for me to tell you what you should or shouldn't do, but I just wanted to share something that happened a couple of weeks ago. My wife helped a young couple who were in a similar situation to yours, but they were already in France. They had been refused entry at the France/Spain border and were staying in a hotel, terrified that the hotel may close. My wife drafted letters to their Spanish lawyer and also to the wife's UK employer, detailing why the couple fitted into the "Exceptions" category, and requesting that each provide a letter to support their case for entry. Like you, they had sold their property in the UK, had a home to go to in Spain, but did not have residency. But, the wife had a job to come to in Spain. They then went to the Port Bou crossing where, armed with the additional paperwork, they were granted entry, but this was on 23 March. Even then, they were stopped by the police twice en route to their Spanish property.
Although the ferries aren't running, I believe the chunnel is and the French authorities require you to have completed an "attestation" to carry with you, justifying your journey. Based on what my wife did with the other couple, I'd recommend you obtain a letter of support from your UK lawyer, confirming sale of your UK property, and also from your Spanish lawyer, confirming that your Spanish property is your primary residence. Be prepared to have to try several crossing points from France to Spain and, should France close its hotels, consider whether it's feasible for you to sleep in whatever transport you're coming over in - and, if all else fails, that you're able to return to the UK.
Good luck!